__PHYS 2010__** Sample Exam for CH’s 5 & 6
**

**1]** A 2.50 gm bullet passes through a material
that is 1.25 cm thick. The bullet enters

the material with a velocity of
350 m/s and exits the material with a velocity of 250 m/s.

Find the work done on the bullet
by friction as it passes through the material and the

average force of friction on the
bullet.

Answer: W(fric) = - 75.0 J F(fric) = 6000 N

**2]** A 2.00 kg block sliding
down a frictionless ramp has a velocity of 0.50 m/s when at a

height ,
h , above a level surface. The block slides to the bottom of the ramp and
continues

to slide a short
distance along a level (frictionless) surface until it comes to rest after

compressing a spring a distance
of 1.50 cm. The spring constant is k = 4.6 x 10^{4} N/m.

Find the height, h , for the block. {NOTE: the angle of the ramp and length of
the ramp are

unknown!}

Answer: 0.25 m

**3]** The concept of "impulse" is often used
when dealing with the impact forces involved in

collisions. Two darts are thrown
with the same speed at a standing block of wood. Although

they are identical in mass, one
dart has a pointed tip (it sticks in the wood) while the other

has a rubber tip (it bounces back
from the wood). Explain which dart will be more successful

in providing the force necessary
to knock over the block of wood using the concept of

impulse
to justify your reasoning.

Answer: Need to **show** impulse
provided by rubber dart will be twice that of pointed tip dart!

**4]** Ball 1 (mass = 2.0 kg)
travels to the right with a speed of 12 m/s. It has a head-on,**
**__inelastic__

__collision__ with Ball 2 (mass = 6.0 kg) which is traveling to the left with
a speed of 4.0 m/s.

__The balls
do not sticktogether__ ; they recoil from each other. Ball 1 recoils with a speed
of 8.0 m/s.

What was the impulse
imparted to Ball 2 ?

Answer: 40 N x sec (opposite
initial vel. direction) *[will **need to find**
final vel. of ball 2 = 2.7 m/s]

**5]** You build a device which powers a light
bulb with the energy produced by falling steel balls. The

balls will fall from a height of
4.9 m and take 1.0 s to fall. If the average power developed by gravity

with each falling ball is to be
60 Watts, what must be the mass of a ball?

Answer: 1.2 kg

GENERAL PHYSICS
I **EXAM
3**
NAME_______________________________________

1] A skier with a mass of 60.0 kg has a speed of 3.50
m/s when they are at a vertical height 24.0 m

above the bottom of a hill. If a
constant frictional force of 70.0 N opposes their motion down the

hill and the length of the slope
is 65.0 m, what is their speed at the bottom of the hill?

Answer: 18.2 m/s

2] A spring with spring constant k = 75.0 N/m is used
to launch a projectile of mass 100 gm straight

up. If the spring is compressed
12.5 cm in order to launch the projectile, how high above this

compressed spring point is the
projectile when it has a speed of +1.50 m/s? (Neglect friction for

this problem!)

Answer: 0.483 m

3] A) A 10.0 kg object that is moving to
the right with a constant velocity collides head-on with

a 15.0 kg object that is
initially at rest. The two objects stick together and move off to the right

with a velocity of 8.00 cm/s.
What was the initial velocity (don’t forget
direction!) of the

10.0 kg
object?

Answer: 20.0 cm/s to the right

B) Now the stuck
together masses moving to the right as one object have an elastic head-on

collision with a 25.0 kg mass
that is at rest. Give the final velocities of both objects (the stuck

together masses and the 25 kg
mass) after the collision.

Answer: stuck
together, v = 0
cm/s
25 kg mass, v = 8.00 cm/s to the right

4] A baseball of mass 0.14 kg has an
initial velocity of 38 m/s as it approaches the bat. The bat

applies a force very much larger
than the weight of the ball and the ball departs from the bat

with a final velocity of 58 m/s
in a direction __exactly opposite__ to its initial velocity. If the contact

time between the bat and the ball
is 4.0 x 10^{-3} s, what is the average force exerted on the ball

by the bat?

Answer: 3360 N

**SAMPLE MULTIPLE CHOICE**

1) According to the scientific definition of work, pushing on a rock accomplishes no

work unless there is

A) an applied force greater than its weight.

B) a net force greater than zero.

C) an opposing force.

D) movement in the same direction as the force.

2) The potential energy of a box on a shelf, relative to the floor, is a measure of

A) the work done putting the box on the shelf from the floor.

B) the weight of the box times the distance above the floor.

C) the energy the box has because of its position above the floor.

D) any of these

3) Which quantity has the greatest influence on the amount of kinetic energy that a large

truck has while moving down the highway?

A) mass

B) weight

C) velocity

D) size

4) The law of conservation of energy is a statement that

A) energy must be conserved and you are breaking a law if you waste energy.

B) the supply of energy is limited so we must conserve.

C) the total amount of energy is constant.

D) energy cannot be used faster than it is created.

5) It is correct to say that impulse is equal to

A) momentum

B) the change in momentum

C) the force multiplied by the distance the force acts

D) all the above (A, B, and C)

E) none of the above (A, B, or C)

6) A bullet is fired from a gun. The speed of the bullet will be about the same as the speed of the recoiling gun

A) as long as momentum is conserved.

B) because velocity will be conserved.

C) because both velocity and momentum are conserved.

D) only if the mass of the bullet is about the same as the mass of the gun.

E) none of the above are correct

7) Compared with falling on a wooden floor, a wine glass may not break when it falls on a carpeted floor because

A) the impulse imparted to it will be smaller.

B) the time during which the stopping force is applied will be longer.

C) both A) and B) are true.

D) neither A) nor B) are true.

8) The force that accelerates a rocket in deep space is exerted on the rocket by

A) the rocket’s engine.

B) atmospheric pressure.

C) the rocket’s momentum.

D) the exhaust gas from the engine.

E) none of the above

**SAMPLE MULTIPLE CHOICE QUESTIONS FOR
CH’s 5
& 6 ANSWERS**1)
d

2)
d

3)
c

4)
c

5)
b

6)
d

7)
b

8) d