Physics Exam 3

An astronaut whose total mass is 100 kg ejects 1.0 g of gas from his propulsion pistol at aspeed of 50 m/s. His recoil speed is a. 0.5 mm/s b. 5 mm/s c. 5 cm/s d. 50 cm/s

0.5

A 30-kg girl and a 25-kg boy face each other on frictionless roller skates. The girl pushesthe boy, who moves away at a speed of 1.0 m/s. The girl's speed is a. 0.45/ms b. 0.55 m/s c. 0.83 m/s d. 1.2 m/s

0.83

A stationary 60-g tennis ball is struck by a racket that exerts an average force of 300 N onit for a time of 0.0050s. The KE of the ball after the impact is a. 0.019J b. 0.068 J c. 1.5 J d. 19 J

19

A 200-g ball moving at 5.0 m/s strikes a wall perpendicularly and rebounds elastically at the same speed. The impulse given to the wall is a. 1Ns b. 2 Ns c. 5 Ns d. 10 Ns

2

A 1200-kg car moving north at 50 km/h collides with a 1600-kg car moving east at 30km/h. The cars stick together, and the wreckage moves off at an initial speed of a. 27 km/h b. 38 km/h c. 39 km/h d. 58 km/h

27

A ball whose momentum is p strikes a wall and bounces off. The change in the ball's momentum is a. 0 b. p c. 2p d. 3p

2p

The direction in which the wreckage of the preceding collision moves off is a. 39 o E of N b. 45 o E of N c. 51 o E of N d. 54 o E of N

39

An 800-kg car moving at 80 km/h crashes into a 1200 kg car initially moving at 40 km/hin the same direction. If the two cars stick together, the wreckage has an initial speed of a. 8 km/h b. 40 km/h c. 56 km/h d. 60 km/h

56

Average momentum of 70 kg runner who covers 400 m in 50 s is: a) 8.75 kg.m/s b) 57 kg.m/s c) 560 kg.m/s d) 5488 kg.m/s

560

Consider the cars in the previous question. Now they are moving in toward each otherand collide head-on. If they stick together, the wreckage now has an initial speed of a. 8 km/h b. 40 km/h c. 56 km/h d. 60 km/h

8

In an elastic collision a. momentum is conserved but not KE b. KE is conserved but not momentum c. momentum and KE are both conserved d. neither momentum nor KE is conserved

Both momentum and KE are conserved

In the previous two questions, we have a rear-end collision and a head-on collision.Which of the following is correct? a. There was NO kinetic energy lost in either collision. b. Less KE was lost in the rear-end collision than in the head-on collision. c. More KE was lost in the rear-end collision than in the head-on collision. d. KE was lost, but the same amount was lost in both collisions.

Less KE was lost in the rear-end collision than in the head-on collision

In an inelastic collision a. momentum is conserved but not KE b. KE is conserved but not momentum c. momentum and KE are both conserved d. neither momentum nor KE is conserved

Momentum is conserved but not KE

momentum can be expressed in

N*s

An iron sphere of mass 30kg has the same diameter as an aluminum sphere of mass 10.5kg. The spheres are simultaneously dropped from a cliff. When they are 10m from the ground they have identical

acceleration

change in momentum is most closely related to

impulse

an object that has momentum must also have

kinetic energy

If a shell fired from a cannon explodes in midair, a. its total momentum increases b. its total momentum decreases c. its total kinetic energy increases d. its total kinetic energy decreases

kinetic energy increases

An object at rest may have

potential energy

An object in motion need not have

potential energy

When the velocity of a moving object is doubled

the momentum is double

What never changes when two or more objects collide is a. the momentum of each one b. the kinetic energy of each one c. the total momentum of all the objects d. the total kinetic energy of all the objects

the total momentum of all objects