# m-radius Ferris wheel rotates once each 32 s angular speed

40,594 results

**physics**

Two gerbils run in place with a linear speed of 0.60m/s on an exercise wheel that is shaped like a hoop.Find the angular momentum of the system if each gerbil has a mass of 0.22kg and the exercise wheel has a radius of 8.5 cm and a mass of 5.0 g.

**Physics**

A Ferris wheel has a circumference of 93 m and it completes one rotation in 2.3 minutes without stopping. What is the percentage change in apparent weight (=weight difference/weight = W/W) of a passenger between the highest and the lowest positions on this Ferris wheel?

**physics**

A flywheel rotates at a constant angular acceleration. At time t = 1.38 s, it rotates with a speed of ω = 2.40 rad/s in the clockwise direction. At time t = 5.97 s, it rotates with a speed of ω = 2.40 rad/s in the counter-clockwise direction. What is its angular ...

**Math**

Shirley is on a Ferris wheel which spins at the rate of 3.6 revolutions per minute. The wheel has a radius of 35 feet, and the center of the wheel is 51 feet above the ground. After the wheel starts moving, Shirley takes 12 seconds to reach the top of the wheel. How high above...

**physics**

A car's wheel of radius r=50cm goes through 5000rev in 1min. find the car's average angular velocity,and how far it travels along the ground in 1min. The linear speed v and angular speed w of the point of a rotating body are connected by the equation v=wr. where r is the ...

**Physics**

A space station in the form of a large wheel, 200m in diameter, rotates to provide an "artificial gravity" of 9.9m/s^2 for people located at the outer rim. What is the frequency of the rotational motion for the wheel to produce this effect? Answer in units of rev/min. ...

**Trig**

A ferris wheel has a 14 meter diameter and turns counterclockwise at 6 rpm. a) Assuming that the center of the wheel is the origin of an x-y coordinate plane, write functions to find the position (x,y) of a rider that starts at the bottom of the wheel. b) Where is the rider 2 ...

**Physics. PLEASE HELP!!**

A Ferris wheel rotates 4 times each minute and has a diameter of 17 m. The acceleration of gravity is 9.8 m/s2. What is the centripetal acceleration of a rider? Answer in units of m/s2

**Physics. PLEASE HELP!!**

A Ferris wheel rotates 4 times each minute and has a diameter of 17 m. The acceleration of gravity is 9.8 m/s2. What is the centripetal acceleration of a rider? Answer in units of m/s2

**Physics**

A rotating wheel requires 8.00 s to rotate 29.0 revolutions. Its angular velocity at the end of the 8.00 s interval is 95.0 rad/s. What is the constant angular acceleration of the wheel? (Do not assume that the wheel starts at rest.)

**Physics**

A 16 kg mass is attached to a cord that is wrapped around a wheel with a radius of 10.9cm. The acceleration of the mass down the frictionless incline is measured to be 1.4 m/s2.The angle of incline is 36 degrees. Assume the axle of the wheel to be frictionless. The force of ...

**science**

please help...A wheel 1.0m in diameter is rotating about a fixed axis with an initial angular velocity of 2rev.s-1.the angular acceleration is 3rev.s-1. (1)compute the angular velocity after 6s. (2)through what angle has the wheel turned in this time interval? (3)what is the ...

**physics**

A spoked wheel with a radius of 44.0 cm and a mass of 1.90 kg is mounted horizontally on frictionless bearings. JiaJun puts his 0.550-kg guinea pig on the outer edge of the wheel. The guinea pig begins to run along the edge of the wheel with a speed of 18.0 cm/s with respect ...

**math**

The London Eye is a large ferris wheel. Each sealed and air-conditioned passenger capsule holds about 25 passengers. The diameter of the wheel is 135 m, and the wheel takes about half an hour to complete one revolution. a) Determine the exact angle, in radians, that a ...

**math**

The London Eye is a large ferris wheel. Each sealed and air-conditioned passenger capsule holds about 25 passengers. The diameter of the wheel is 135 m, and the wheel takes about half an hour to complete one revolution. a) Determine the exact angle, in radians, that a ...

**physics**

An automobile tire has a radius of 0.335 m, and its center moves forward with a linear speed of v = 24.1 m/s. (a) Determine the angular speed of the wheel. (b) Relative to the axle, what is the tangential speed of a point located 0.243 m from the axle?

**PHYSICS**

AN AUTOMOBILE TIRE HAS A RADIUS OF 0.330M AND ITS CENTER MOVES FORWARD WITH A LINEAR SPEED OF V= 15.0M/S. a) DETERMINE THE ANGULAR SPEED OF THE WHEEL. B) RELATIVE TO THE AXLE, WHAT IS THE TANGENTIAL SPEED OF A POINT LOCATED 0.175M FROM THE AXLE?

**Physics**

A potter's wheel rotates with an angular frequency of 1.54 rad/s. What is its period?

**Physics**

a) Find the angular velocity of a 40 cm radius wheel that is moving at 20 m/s. b) How many times will this wheel rotate in 5 seconds?

**PHYSICS2, help!**

A string is wrapped around the rim of a flywheel 0.400 m in radius, and a steady pull of 50.0 N is exerted on the cord. The wheel is mounted in frictionless bearings on a horizontal shaft through it's center. The moment of inertia of the wheel is 4.00 kg.m^2 .Calculate the ...

**PHYSICS**

A string is wrapped around the rim of a flywheel 0.400 m in radius, and a steady pull of 50.0 N is exerted on the cord. The wheel is mounted in frictionless bearings on a horizontal shaft through it's center. The moment of inertia of the wheel is 4.00 kg.m^2 .Calculate the ...

**Physics**

At time t=0 a grinding wheel has an angular velocity of 26.0 rad/s. It has a constant angular acceleration of 25.0 rad/s^2 until a circuit breaker trips at time t = 2.50 s. From then on, the wheel turns through an angle of 440 rad as it coasts to a stop at constant angular ...

**Trig - Ferris Wheel**

A ferris wheel is 250 ft in diameter and revolves every 40 second when in motion. You step up to the seat on the wheel at the bottom 2 feet about the fround so you are sitting 4 feet about the ground at start. Derive the formula for the height of your seat at time (t). Then ...

**Physics**

When a solid wheel rotates about a fixed axis, do all of the points of the wheel have the same tangential speed?

**Physics**

A rotating wheel requires 9.00 s to rotate 29.0 revolutions. Its angular velocity at the end of the 9.00 s interval is 98.0 rad/s. What is the constant angular acceleration of the wheel in radians/second squared? (Do not assume that the wheel starts at rest.)

**physics**

A torque of 0.97 N-m is applied to a bicycle wheel of radius 0.35 m and mass 0.75 kg. Treating the wheel as a hoop, find its angular acceleration.

**Physics**

a track is mounted on a large wheel that is free to turn with negligible friction about a vertical axis. a toy train of mass m is placed on the track and, with the system initially at rest, the electrical power is turned on. the train reaches a steady speed v with respect to ...

**Physics**

I've been stuck on this problem for a while. Im not sure where to even begin. A bike wheel is rotating with an angular velocity of 3.1 rev/s. If the coefficient of kinetic friction between the wheel and brakes is .87, then find the revolutions the wheel makes in coming to rest...

**physics**

A beetle sits at the top of a bicycle wheel and flies away just before it would be squashed. Assuming that the wheel turns clockwise, the beetle's angular displacement is 3.14 radians, which corresponds to an arc length of 1.2 m. What is the wheel's radius?

**Physics**

A potter’s wheel of radius 53.13 cm and mass 106.4 kg is freely rotating at 47.1 rev/min. The potter can stop the wheel in 5.65 s by pressing a wet rag against the rim and exerting a radially inward force of 66.2 N. What is the angular acceleration of the wheel?

**science- physics**

A rotating wheel requires 4.17 s to rotate through 37 rev. Its angular speed at the end of the 4.17 s interval is 104 rad/s. What is its constant angular acceleration? Assume the angular acceleration has the same sign as the angular velocity.

**Physics**

A bicycle wheel of radius .7m is rolling without slipping on a horizontal surface with an angular speed of 2 rev/s when the cyclist begins to uniformly apply the brakes. The bicycle stops in 5 s. Through how many revolutions did the wheel turn during the 5 s of braking? I ...

**Physics**

A bicycle wheel of radius .7m is rolling without slipping on a horizontal surface with an angular speed of 2 rev/s when the cyclist begins to uniformly apply the brakes. The bicycle stops in 5 s. Through how many revolutions did the wheel turn during the 5 s of braking? I ...

**Physics**

A bicycle wheel of radius .7m is rolling without slipping on a horizontal surface with an angular speed of 2 rev/s when the cyclist begins to uniformly apply the brakes. The bicycle stops in 5 s. Through how many revolutions did the wheel turn during the 5 s of braking? I ...

**Physics**

A hoop of mass M = 3 kg and radius R = 0.5 m rolls without slipping down a hill, as shown in the figure. The lack of slipping means that when the center of mass of the hoop has speed v, the tangential speed of the hoop relative to the center of mass is also equal to vCM, since...

**science**

A hoop of mass M = 4 kg and radius R = 0.4 m rolls without slipping down a hill, as shown in the figure. The lack of slipping means that when the center of mass of the hoop has speed v, the tangential speed of the hoop relative to the center of mass is also equal to vCM, since...

**physics**

A star the size of the sun has a mass 8 times as great. It rotates on its axis once every 12 days. It then collapses into a neutron star of radius 10km, losing three quarters of its mass in the process. How long does it take to rotate once after collapse? (it's spere though ...

**physics help please....**

After fixing a flat tire on a bicycle you give the wheel a spin. (a) If its initial angular speed was 5.17 rad/s and it rotated 10.6 revolutions before coming to rest, what was its average angular acceleration? rad/s2 (b) For what length of time did the wheel rotate? s

**physics**

A large grinding wheel in the shape of a solid cylinder of radius 0.330 m is free to rotate on a frictionless, vertical axle. A constant tangential force of 210 N applied to its edge causes the wheel to have an angular acceleration of 1.161 rad/s2. (b) What is the mass of the ...

**Physics**

An automobile tire has a radius of 0.380 m, and its center moves forward with a linear speed of v = 19.0 m/s. (a) Determine the angular speed of the wheel. (Assume that there is no slipping of the surfaces in contact during the rolling motion.) rad/s

**trig**

How fast is a bicycle traveling in feet per second if a wheel has a 21-in. diameter and the angular speed of the wheel is 33 radians per second? The speed of the bicycle is the same as the linear speed of a wheel.

**math-precalculus**

A Ferris wheel is 50 meters in diameter and boarded from a platform that is 1 meters above the ground. The six o'clock position on the Ferris wheel is level with the loading platform. The wheel completes 1 full revolution in 6 minutes. How many minutes of the ride are spent ...

**physics**

A wheel is rotating at a rate of 2.2 revolutions every 3.5 s. Through what angle, in radians, does the wheel rotate in 1.0 Angular displacement=angularspeed*time angular speed has to be in radians/sec, and time in seconds.

**Trig**

A Ferris wheel is 40 meters in diameter and boarded from a platform that is 4 meters above the ground. The six o'clock position on the Ferris wheel is level with the loading platform. The wheel completes 1 full revolution in 2 minutes. How many minutes of the ride are spent ...

**precalculus**

A Ferris wheel is 10 meters in diameter and boarded from a platform that is 3 meters above the ground. The six o'clock position on the Ferris wheel is level with the loading platform. The wheel completes 1 full revolution in 4 minutes. How many minutes of the ride are spent ...

**Physics**

In a fairground ride a child of mass 37 kg stands against the inside surface of a circular cylinder of radius 3.9m that rotates around its vertical axis of symmetry. The cylinder has an angular speed of 1.3 rad/s and an angular acceleration of 0.12 rad s^-2. What is the radial...

**Physics**

A cyclist starts from rest and pedals such that the wheels of his bike have a constant angular acceleration. After 20.0 s, the wheels have made 219 rev. What is the angular acceleration of the wheels? What is the angular velocity of the wheels after 20.0 s? If the radius of ...

**physics**

A cyclist starts from rest and pedals such that the wheels of his bike have a constant angular acceleration. After 18.0 s, the wheels have made 190 rev. What is the angular acceleration of the wheels? What is the angular velocity of the wheels after 18.0 s? If the radius of ...

**grade 12 Functions**

A ferris wheel with a diameter of 60m rotates at a constant speed three times every 1.5pie minutes and reaches a maximum height of 62m from the ground. if you started the ride when it is at its highest point, on what internal of time would you be more than 58m above the ground...

**Physics**

The large disk-shaped flywheel illustrated below has a radius R of 0.25 m. It is made to spin by the small wheel that contacts it at its rim. The small wheel applies a constant force of 1430 N. Friction in the bearing exerts a retarding torque 22 Nm on the large wheel. If the ...

**physics**

A large grinding wheel in the shape of a solid cylinder of radius 0.330 m is free to rotate on a frictionless, vertical axle. A constant tangential force of 210 N applied to its edge causes the wheel to have an angular acceleration of 1.161 rad/s2. (a) What is the moment of ...

**physics**

A large grinding wheel in the shape of a solid cylinder of radius 0.370m is free to rotate on a frictionless, vertical axle. A constant tangential force of 470 N applied to its edge causes the wheel to have an angular acceleration of 0.800 rad/s2. (a) What is the moment of ...

**physics**

a 60kg man is on a steadily rotating Ferris wheel. the man is standing on a bathroom scale and the scale reads 45kg at the top of the wheel. take g=10m/s^2 (a) what does the scale read when the man is at the bottom of the wheel? (b)what does the scale read when the man is ...

**Physics 1**

A disk rotates with constant angular acceleration. The initial angular speed of the disk is 2π rad/s. After the disk rotates through 17π radians, the angular speed is 18π rad/s. (a) What is the magnitude of the angular acceleration? answer in rad/s2 (b) How much...

**math function2**

A ferris wheel turns at a constant speed. the lowest point of the wheel is ground level. a person is standing on a platform 4m about ground. The intervals between two successive times are alternatly 6 s and 18 s. Part A) what is the period of rotation? Part B) what is the ...

**Pre-Cal**

A Ferris wheel is 40 meters in diameter and boarded from a platform that is 5 meters above the ground. The six o'clock position on the Ferris wheel is level with the loading platform. The wheel completes one full revolution every 7 minutes. You make two complete revolutions on...

**PHYSICS**

A spinning wheel on a fireworks display is initially rotating in a counterclockwise direction. The wheel has an angular acceleration of -3.80 rad/s2. Because of this acceleration, the angular velocity of the wheel changes from its initial value to a final value of -21.0 rad/s...

**PHysics**

A thin, light wire is wrapped around the rim of a wheel, as shown in the following figure. The wheel rotates without friction about a stationary horizontal axis that passes through the center of the wheel. The wheel is a uniform disk with radius 0.400 m. An object of mass 4.50...

**Maths**

A ferris wheel has an axle standing 38m off the ground and a radius of 35m. The wheel takes 5 minutes to complete one revolution. The wheel moves in clockwise motion and you are sitting in one of the carriages which is horizontally in line with the axle, moving upwards. Form ...

**physics**

an airplane propeller slows from an initial angular speed of 12.5rev/s to a final angular speed of 5rev/s during the process the propeller rotates through 21 rev. find the angular acceleration of the propeller if in radians per second squared, assuming its constant?

**Physics**

A penny farthing is a bicylce that was popular between 1870 and 1890. As the drawing shows, this type of bicycle has a large front wheel (R=1.20m) and a smaller rear wheel (r=.34m). A bicyclist, riding at a linear velocity of 12.5 m/s, applies the brake and produces an angular...

**Trig**

As you ride a ferris wheel, your distance from the ground varies sinusoidally with time. When the last passenger boards the ferris wheel and the ride starts moving, let your position be modeled by the diagram provided. Let t be the number of seconds that have elapsed since you...

**Pre-Calculus**

a ferris wheel is elevated 1 meter above ground. When car reaches the highest point of the Ferris wheel, it's altitude from ground level is 31 metres. How far away from the center, horizontally, is the car when it is at an altitude of 25 meters?

**physics**

Point P is on the rim of a wheel of radius 2.0 m. At time t = 0, the wheel is at rest, and P is on the x axis. The wheel undergoes a uniform angular acceleration of 0.01 rad/s^2 about the center O. In Figure 9.1, the magnitude of the linear acceleration of P, when it reaches ...

**physics**

A conveyer belt is driven by a large (diameter = 1.0 m) wheel. The wheel starts from rest and has an angular acceleration of 0.35 rad/s 2. (a) Through what angle does the wheel turn in 18 s? (b) What is the wheel's angular velocity at that time...

**physics**

A 4.50-kg wheel that is 34.5 cm in diameter rotates through an angle of 13.8 rad as it slows down uniformly from 22.0 rad/s to 13.5 rad/s. What is the magnitude of the angular acceleration of the wheel? A) 0.616 rad/s 2 B) 22.5 rad/s 2 C) 5.45 rad/s 2 D) 10.9 rad/s 2 E) 111 ...

**physics**

An automobile wheel with a 9.00-cm radius and the radius to the rim is 7cm, as shown below, rotates at 2.50 rad/s. How fast does a point 6.50 cm from the center travel? 1 cm/s

**Physics**

A device consists of eight balls each of mass 0.4 kg attached to the ends of low-mass spokes of length 1.8 m, so the radius of rotation of the balls is 0.9 m. The device is mounted in the vertical plane. The axle is held up by supports that are not shown, and the wheel is free...

**Physics**

In a tape recorder, the magnetic tape moves at a constant linear speed of 5.6 cm/s. To maintain this constant linear speed, the angular speed of the driving spool (the take-up spool) has to change accordingly. (a) What is the angular speed of the take-up spool when it is empty...

**Physics**

A grindstone of radius 4.0m is initially spinning with an angular speed of 8.0 rad/s. The angular speed is then increased to 12 rad/s over 4.0s. Assume that the angular acceleration is constant. What is the average angular speed of grindstone?

**Math - need help ASAP!! Please!**

The question relates to application of sine functions. -------------- A carnival Ferris wheel with a radius of 7m makes one complete revolution every 16 seconds. The bottom of the wheel is 1.5m above the ground. a) Draw a sketch to show a person's height (h) above the ground ...

**physics**

A small bead of mass m is carried by a circular hoop of radius r which rotates about a fixed vertical axis. Show how one might determine the angular speed w of the hoop by observing the angle theta which locates the bead. Theta is measured to the right of the vertical axis. ...

**Math**

A ferris wheel is 30 meters in diameter and boarded in the six o'clock position from a platform that is 10 meters above the ground. The wheel completes one full revolution every 10 minutes. At the initial time t=0 you are in the twelve o'clock position.Find a formula, using ...

**Physics**

A centrifuge in a medical laboratory rotates at an angular speed of 3500 rpm (revolutions per minute). When switched off, it rotates 70.0 times before coming to rest. Find the constant angular acceleration of the centrifuge. (Assume the initial direction of rotation is the ...

**math trig**

If a ferris wheel has a radius of 20.5meters, how tall would a 45 degree angle be?

**Advanced Physic**

A gob of clay, mass 217 g, falls from rest a distance 50 cm before striking and sticking to the edge of a wheel free to rotate about a horizontal axis through its center (Fig. 10-38). The wheel can be approximated as a solid disk of mass 49 kg and radius 84 cm. What is the ...

**physics**

Each of the following objects has a radius of 0.180 m and a mass of 2.65 kg, and each rotates about an axis through its center (as in the table below) with an angular speed of 41.4 rad/s. Find the magnitude of the angular momentum of each object. a) a hoop ___ kg m/s b) a ...

**physics**

Each of the following objects has a radius of 0.180 m and a mass of 2.65 kg, and each rotates about an axis through its center (as in the table below) with an angular speed of 41.4 rad/s. Find the magnitude of the angular momentum of each object. a) a hoop ___ kg m/s b) a ...

**Math**

1. What percent of people chose the Ferris wheel or the carousel as their favorite ride? Other 19% Ferris wheel 18% Carousel 25% Roller coaster 38% A. 25% B. 37% C. 43% < -- C? D. 56% 2. Two hundred people were surveyed about their favorite ride at an amusement park. The ...

**physics**

A high-speed sander has a disk 8.00 cm in radius that rotates about its axis at a constant rate of 1100 revolutions per minute. Determine the angular speed of the disk in radians per second.

**Math (please help!)**

The largest Ferris Wheel in the world is the London Eye in England. The height (in metres) of a rider on the London Eye after t minutes can be described by the function h(t) = 67 sin[0.2094(t-30)] + 70 Using this equation i'm supposed to find the diameter, the maximum (top of ...

**Advanced Functions**

The vertical position, h, in metres, of a gondola on a Ferris wheel is modelled using the function h = 10 sin ((pi/15) (t-d)) + 12 where t is the time, in seconds. The gondola must assume a vertical position of 7 m at t=0 s , and be on its way upward. Determine the phase shift...

**math**

The Earth rotates once every 24 hours. What is the angular speed of a point on the Earth's surface in rad/min. Give your answer to five decimal places. Use 3.14 for pi. (example units: m/s, mi/h)

**Dynamics**

A pelton wheel attains its operating speed of 800 rev/min within 2s after it is turn on. Determine the constant angular accelerations of pelton wheel. also find the total number of revolutions the wheel makes before it attains operating speed

**Math**

You are in a car of a ferris wheel. The wheel has a radius of 8m and turns counterclockwise. Let the orgin be at the center of the wheel. Begin each sketch in parts a) and b) when the radius from the centre of the wheel to your car is along the positive x-axis. a) Sketch the ...

**Physics**

A Ferris Wheel with a radius of 15 meter makes one complete rotation every 10 seconds.

**Math 142 (Pre-Cal) (Circles)**

A wheel has a radius of 10 inches is rotating with an angular velocity of 2.5 revolutions per second. Find the distance the wheel travels in 15 seconds.

**Physics**

a bicycle turned upside down whiles owner repairs a flat tire. A friend spins the other wheel, of radius R, and observed that drops of water fly off tangentially. She measures the height reached by drops vertically. A drop that breaks loose from the tire on one turn rises a ...

**Physics**

1. A point on the edge of a large wheel of radius 0.45 meters moves through an angle of 170o at a constant angular velocity of 0.25 radians/sec. . (a) Find the length (in meters) of the arc described by the point. (b) Find the linear velocity (in m/sec) of a point located on ...

**physics**

questions( there are 3 so I will # 1-3) info: A 18.9 kg object is attached to a cord that is wrapped around a wheel of radius 10.7 cm. The acceleration of the object down the frictionless incline is measured to be .9 m/s2. Assume the axle of the wheel to be frictionless. The ...

**Physics**

The angular velocity of a wheel is given by w(t) = (2.00 rad/s^2)t + (1.00 rad/s^4)t^3. A. What is the angular displacement of the wheel from time t=0.00s to time t=T? B.What is the angular acceleration of the wheel as a function of time?

**Physics**

The angular velocity of a wheel is given by w(t) = (2.00 rad/s^2)t + (1.00 rad/s^4)t^3. A. What is the angular displacement of the wheel from time t=0.00s to time t=T? B.What is the angular acceleration of the wheel as a function of time?

**physics**

A bicycle is rolling down a circular portion of a path; this portion of the path has a radius of 8.73 m. As the drawing illustrates, the angular displacement of the bicycle is θ = 0.979 rad. What is the angle (in radians) through which each bicycle wheel (radius = 0.320 m...

**Angular acceleration**

Appreciate if someone can advise on how to calculate the following: A hoist lifts a 3.5kg load from rest, and has a final velocity of 2 m/s after 4 seconds. The motor can develop a torque of 4 Nm. Determine: i) The linear acceleration of the mass. ii) The angular acceleration ...

**science**

A flywheel makes 120 rpm. Find the angular speed of any point on the wheel and linear speed of a point is 10 cm from the center of the wheel.

**Physics**

Starting from rest, a disk rotates about its central axis with constant angular acceleration. In 6.00 s, it rotates 28.0 rad. During that time, what are the magnitudes of (a) the angular acceleration and (b) the average angular velocity? (c) What is the instantaneous angular ...

**Math**

If a Ferris wheel has a 64 m radius and the center ot the wheel is 84 m above the ground, what is the height of a carriage above the ground starting from 0 degrees to 360 degrees?

**angular accleration**

a wheel if a vehical rotates uniformly at the rate if 120 rotations per mint suddenly it goes faster and reaches 150 rotations per mint after 30s find the angular acc

**College Physics**

A wheel of radius 0.398 m is mounted on a frictionless horizontal axis. The rotational inertia of the wheel about the axis is 0.0576 kg·m2. A massless cord wrapped around the wheel is attached to a 0.790 kg block that slides on a horizontal frictionless surface. If a ...

**physics**

A large wooden wheel of radius R and the moment of inertia I is mounted on an axle so as to rotate freely. A bullet of mass m and speed v is shot tangential to the wheel and strike its edge, lodging in the wheel’s rim. If the wheel was originally at rest, what is its ...