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February 28, 2015

February 28, 2015

Posted by **christ** on Monday, January 28, 2013 at 3:32am.

15 m above the top of the building

30 m below the top of the building

15 m below the top of the building

30 m above the building

2 A stone thrown from ground level returns to the same level 4 s after. With what speed was the stone thrown? Take g=10ms−2

20 m/s

10 m/s

30 m/s

15 m/s

3 What is common to the variation in the range and the height of a projectile?

horizontal velocity

time of flight vertical velocity, horizontal acceleration

vertical velocity

horizontal acceleration

4 A cart is moving horizontally along a straight line with constant speed of 30 m/s. A projectile is fired from the moving cart in such a way that it will return to the cart after the cart has moved 80 m. At what speed (relative to the cart) and at what angle (to the horizontal) must the projectile be fired?

35.8 m/s at 24 degrees

38.6 m/s at 54 degrees

27 m/s at 35 degrees

24 m/s at 44 degrees

5 The trajectory of a projectile is

an ellipse

a circle

a parabola

a straight line

6 The motion of a ball rolling down a ramp is one with

constant speed

increasing acceleration

constant acceleration

decreasing acceleration

7 How fast must a ball be rolled along the surface of a 70-cm high table so that when it rolls off the edge it will strike the floor at the same distance (70cm) from the point directly below the edge of the table?

174.5 cm/s

185.2 cm/s

215.3 cm/s

143.7 cm/s

8 A ball is kicked and flies from point P to Q following a parabolic path in which the highest point reached is T. The acceleration of the ball is

zero at T

greatest at P

greatest at T and Q

the same at P as at Q and T

9 A mass accelerates uniformly when the resultant force acting on it

is zero

is constant but not zero

increases uniformly with respect to time

is proportional to the displacement of the mass from a fixed point

10 The term that best describes the need to hold the butt of a riffle firmly against the shoulder when firing to minimise impact on the shoulder is

forward displacement

forward acceleration

recoil velocity

pressure

11 Two trolleys X and Y with momenta 20 Ns and 12 Ns respectively travel along a straight line in opposite directions before collision. After collision the directions of motion of both trolleys are reversed and the magnitude of the momentum of X is 2 Ns. What is the magnitude of the corresponding momentum of Y?

6 Ns

8 Ns

10 Ns

30 Ns

12 A force of 2i+7j N acts on a body of mass 5kg for 10 seconds. The body was initially moving with constant velocity of i−2j m/s. Find the final velocity of the body in m/s, in vector form.

5i+12j

12i−5j

10i−7j

7i+10j

13 The exhaust gas of a rocket is expelled at the rate of 1300 kg/s, at the velocity of 50 000 m/s. Find the thrust on the rocket in newtons

65107

35107

76107

57107

14 Sand drops at the rate of 2000 kg/min. from the bottom of a hopper onto a belt conveyor moving horizontally at 250 m/min. Determine the force needed to drive the conveyor, neglecting friction.

500 N

800 N

139 N

152 N

15 A 30,000-kg truck travelling at 10.0m/s collides with a 1700-kg car travelling at 25m/s in the opposite direction. If they stick together after the collision, how fast and in what direction will they be moving?

8.1 m/s in the direction of the truck's motion

12.3 m/s in the direction of the car's motion

24.2 m/s in the direction of the car's motion

17.6 m/s in the direction of the truck's motion

16 A gun of mass M is used to fire a bullet of mass m. The exit velocity of the bullet is v. Find the recoil velocity of the gun

Mv/m

mv/M

–Mvm

−mvM

17 A 40-g ball travelling to the right at 30 cm/s collides head on with an 80-g ball that is at rest. If the collision is perfectly elastic, find the velocity of each ball after collision

the first ball is going to the right at 10m/s while the other is going to the left at 20m/s

the first ball is going to the left at 10m/s while the other is going to the right at 20m/s

the first ball is going to the left at 20 m/s while the other is going to the right at 10 m/s

the first ball is going to the right at 10 m/s while the other is going to the left at 10 m/s

18 A 10-g bullet of unknown speed is shot horizontally into a 2-kg block of wood suspended from the ceiling by a cord. The bullet hits the block and becomes lodged in it. After the collision, the block and the bullet swing to a height 30cm above the original position. What was the speed of the bullet? (This device is called the ballistic pendulum). Take g=98ms−2

487 m/s

640 m/s

354 m/s

700 m/s

19 How large an average force is required to stop a 1400-kg car in 5.0 s if the car’s initial speed is 25 m/s?

2000 N

3500 N

9000 N

7 000N

20 Which of these is NOT a statement of Newton’s law of universal gravitation?

gravitational force between two particles is attractive as well as repulsive

gravitational force acts along the line joining the two particles

gravitational force is directly proportional to the product of the masses of the particles

gravitational force is inversely proportional to the square of the distance of the particles apart

- phy -
**Henry**, Wednesday, January 30, 2013 at 8:28pm1. V = Vo + g*t.

Tr = (V-Vo)/g = (0-10)/-10 = 1 s. = Rise

time or time to reach max. ht.

Tf = Tr = 1 s. = Fall time or time to fall back to edge of bldg.

3-Tr-Tf = 3-1-1 = 1 s. Below edge of bldg.

d = Vo*t + 0.5g*t^2.

d = 10*1 + 5*1^2 = 15 m. Below top of bldg.

2. Tr = 4/2 = 2 s. = Rise time.

V = Vo + g*t.

Vo = V - g*t = 0 - (-10)*2 = 20 m/s.

3. Vertical Velocity.

4. V*t = 80 m.

30t = 80

T = 2.67 s. = Time in flight.

Tr = T/2 = 2.66/2 = 1.33 s. = Rise time.

Y = Yo + g*t.

Yo = Y-g*t = 0-(-10)*1.33 = 13.3 m/s. =

Ver. component of initial velocity.

tanA = 13.3/30 = 0.443333

A = 24o.

Vo = 30/cos24 = 32.8 m/s @ 24o.

5. Parabola.

6. Constant acceleration.

7. Vo*t + 0.5g*t^2 = 0.7 m.

4.9t^2 = 0.7

t^2 = 0.1429

29Tf = 0.378 s = Fall time or time to hit the floor.

Vx * 0.378 = 0.7 m.

Vx = 1.852 m/s. = 185.2 cm/s.

- phy -
**obi**, Wednesday, October 16, 2013 at 9:29pmyes

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