# 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 of the mass.

I have calculated the linear acceleration to be 0.5 m/s^-2, how can I calculate the angular acceleration from this.

TIA

Your answer for the linear acceleration is correct. The question should have asked what is the angular acceleration of the MOTOR. The mass that is being lifted is not roatating. What rotates is the cylindrical drum of the hoisting pulley.
The work done in 4 seconds, ignoring the moment of inertia of the hoist and friction, is (1/2)(3.5)^2^2 = 7 J

You could assume a radius for that drum, but it will cancel out in the end. Here is another way to use the torque:

(Torque) x (angle of rotation of the hoist pulley wheel) = Work done
Angle of rotation = 7/3.5 = 2 radians

2 = (1/2)*(angular acceleration)* t^2

Actually, the angular acceleration I computed is for the motor shaft where the torque is specified. To compute the angular acceleration anywhere else will require gear transmission ratios. If you were provided with a diagram, one could figure out angular acceleration from the radius of the pulley hoist and the linear acceleration

Thanks for that, but by transposing, shouldn't it be 2 = 0.5 * a * t^2
a = 2/8
a = 0.25 r/s^2

That's what I'm after, the motor shaft angular acceleration. Can you recheck please, as you got 1 rad/s^2, but my calcs give
2 = 0.5 * a * t^2
2 = 0.5 * 4^2 * a
a = 2/8
a = 0.25 r/s^2

1. 👍 0
2. 👎 0
3. 👁 156

## Similar Questions

1. ### exponential equations

The Sign Guys purchased a new hoist for \$1' 500. If this particular hoist has an annual depreciation rate, r, of 15% calculate the value of the machine in 3 years time. Give answer to 2 decimal places.

asked by Anonymous on March 29, 2015
2. ### Math

Sam is hoisting an engine form a pickup truck he is fixing. He hands hoist using 3 rafters on ceiling. Measures the angle the hoist makes at the baseto be 85 degrees and the length across the of chain across rafters to be 80

asked by Eric on January 17, 2017
3. ### trig

an electric hoist is used to life a piece of equipment y = 2.6 feet. the diameter on the hoist is x = 12 inches. find the number of degrees through which the drum must rotate (round to the nearest integer). *I do apologize, there

asked by xiahou on October 21, 2015
4. ### physics

i need help i don't understand how to do this problem so please help me. A student lifts a 5kg chair 0.8m off the floor, walks at a constant speed for a distance 10m, and then puts the chair back down on the floor. calculate the

asked by pinky on November 7, 2011
5. ### physics

in which of the following is the most work being done by roy and which example roy doing no work? a)roy lifts a 5kg radio up 1 meter b) roy holds a 5 kg radio at a height of 1meter for 3 hours. c)roy lifts a 10 kg TV up 1 meter

asked by lisa on May 31, 2012
6. ### Physical Science 2nd Semester

A student lifts a backpack with a force of 50 Newtons. She lifts the backpack 2 meters off the floor. Calculate the work that she has done.

asked by chris on May 24, 2011
7. ### pysc

an object A 2.5kg is traveling at 25meters per second collides head on with a 5kg mass b calculate the velocity of the 5kg mass if 1.the mass b is initially at rest 2.traveling opposite to mass A at 20m/s 3.traveling in the same

asked by shristi on March 5, 2011
8. ### Math/Physics

A block-and-tackle pulley hoist is suspended in a warehouse by ropes of lengths 2 m and 3 m. The hoist weighs 340 N. The ropes, fastened at different heights, make angles of 50° and 38° with the horizontal. Find the tension in

asked by #1 on July 23, 2019
9. ### Physical Science

An electric hoist lifted a load with a mass of 250kg to a height of 80m in 39s , Calculate

asked by Cher on September 30, 2011
10. ### physics

two people carry a heavy electric motor by placing it on a light board 2m long.one person lifts at one end with a force of 700N, and the other lifts the opposite end with a force of 400N.Calculate the weight of the motor and

asked by Anonymous on April 28, 2013

More Similar Questions