Physics 201/211: Test 3

9:30AM Thursday, November 21, 1996

NAME (printed):

Student Number (SSN):

Recitation Section Number :

INSTRUCTIONS:

• Wait for the oral instruction to begin.
• Show all your work in order to qualify for partial credit. Write legibly!
• Assist the graders by placing a box around your final answer.
• You may only use your calculator for simple arithmetic operations.

You may find the following data useful:

, downward.

Note the formula sheet appended to the end of the test.

This test is worth 50 points. Good Luck!

: Multiple Choice. Circle the most suitable answer for each of the questions enumerated below. There is no partial credit for this section. Each question is worth 4 points.

1. Fluffy the dog is in an elevator traveling upward with an acceleration of 3.00g. If Fluffy's mass is 5.00 kg, then what is her apparent weight?

a)

98.0 N.

b)

147 N.

c)

49.0 N.

d)

196 N.

2. A bucket of water with a mass of 9.5 kg is lifted 10 m. What is the work done by gravity during this process?

a)

J.

b)

J.

c)

J.

d)

J.

3. A scary rollercoaster ride has a vertical loop with a radius of 9.60 m. If a car with a mass of 131 kg has a velocity of 12.0 m/s at the top of the loop, then what is the contact force exerted by the track on the car at this point?

a)

1970 N; upward.

b)

1970 N; downward.

c)

681 N; upward.

d)

681 N; downward.

e)

0 N.

4. A toddler plays with his toys on a rough floor. He pushes a block away from him, and then pulls it towards him again along the same path, so that the block is returned to its starting point. What is the work done by friction during this process?

a)

It is nonzero but unknown.

b)

It is zero.

c)

It is mgd, where d is the distance he pushes it away from him.

d)

No answer is possible.

5. Consider two gliders of unequal mass on an air track. The first glider, of mass  , moves to the right with a velocity v. The second glider, of mass  , sits at rest to the right of the first glider. The two gliders collide elastically. If  , then what most properly describes the first glider's resulting motion?

a)

The first glider comes to a stop.

b)

The first glider continues to move to the right.

c)

The first glider moves to the left as a result of the collision.

d)

No answer is possible.

: Problems and Short Answer. Show your work completely to obtain at least partial credit. Read each problem carefully! Each problem is worth 10 points.

6. You are a police officer called to investigate a car accident. No one has been hurt, but you must determine who is to blame. There were no eyewitnesses, and the two drivers, of course, tell you conflicting stories. Driver A says ``Well, I was driving at just under the allowed speed limit through the intersection when this other car comes speeding out of nowhere and hits me!'' Driver B tells you ``Don't listen to this other fellow (Note that this is the edited P201/211 version.)! He's lying! I was driving at just under the allowed speed limit, and this other guy is the one who came speeding out of nowhere and hit me!'' You turn to the physical evidence. From the skidmarks you can tell that the two cars met at right angles and made a completely inelastic collision. The two cars then skidded as a single unit to a stop in 15.0 m, and you know that the coefficient of kinetic friction for rubber on dry pavement is 0.60. The two-car system went off at an angle of 53  , as indicated in the figure. You can assume that the cars are of equal mass. The local speed limit is 35 mph, or 15.7 m/s. a) Use the skidmark information to compute the velocity of the two-car system immediately after the collision. (4 points)

b) Use momentum conservation at the moment of the car crash to compute the initial velocities of the two cars. Who's lying? (6 points)

7. You are the designer of a freeway off-ramp. You would like the ramp to support a velocity v of 120 km/h, so that someone could go 120 km/h without losing control of his car, and you want the ramp's radius R to be 85 m. Use Newton's Laws and your knowledge of circular motion to relate v, R, g, and the tilt  . What minimum tilt must the ramp have in this case? Neglect friction. (10 points)

8. You would like to measure the spring constant k of a spring, so that you devise the apparatus shown in the figure. The surface on which the apparatus sits is frictionless. Note that m is 0.018 kg, whereas M is 1.2 kg. Originally the spring is compressed .35 m. When the spring is released, the bullet embeds itself in the wooden block, and the combined bullet-block system rises to a maximum height of 0.053 m above the surface. Ignore the friction and mass of the spring. Assume that the bullet-block collision time is short enough to make the effect of external forces during the collision negligible. What is the spring constant k? (10 points)
 

 
Thu Jan 30 14:48:36 EST 1997