PHYS 2010     Sample Exam for CHís  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 104 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 (donít 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 rocketís engine.

  B) atmospheric pressure.

  C) the rocketís momentum.

  D) the exhaust gas from the engine.

  E)  none of the above

 

 

 

SAMPLE MULTIPLE CHOICE QUESTIONS FOR CHís  5 & 6
ANSWERS

1)   d                                                                                                                                                                                                                           

2)  d

3)  c

4)  c

5)  b

6)  d 

7)  b

8) d