Name:
Section:

Physics 121

First Exam

September 30, 2004



Instructions: Answer all three questions on these sheets. Each question counts 30 points. 10 points for legiblyfilling in your name above, last name first.

Problem I is standard multiple-choice, graded only by chosen answer, no further explanation needed.

For Problem II, draw graphs so we can tell whether a line is straight or curved, horizontal or slanted, and explain your reasoning in the space provided.

For Problem III show your work, including any equations you used, or explain in words how you arrived at numerical answers

The exam lasts 50 minutes. Please hand in all four pages of your paper according to the initial letter of your last name, using the alphabetical trays.

Possibly useful formulas

Note that no such table will be on the 2005 exam. Instead you may bring a sheet of your own with formulas
sinq = side opposite q
hypotenuse
              cosq = side adjacent to q
hypotenuse
v = v0 + at               Dx = v0t + 1/2 a t2               v2 = v02 + 2 a Dx
å
 		F = ma               w = mg               g = 9.8 m/s2


















I. Multiple choice. Mark your answer any way you like, and then copy the answer letter in the table below.

  1. On planet Z, the standard unit of length is the foose. Ann the Astronaut is 6 feet tall on earth. She lands on planet Z and is measured to be 90 foosi tall. Her partner Rachael is 81 foosi tall (10% shorter than Ann). How tall is Rachael on Earth?
    1. 5.2 feet           C. 5.8 feet
    2. 5.4 feet           D. 6.3 feet
  2. Two objects of different mass are released simultaneously from the top of a 20-m tower and fall to the ground. If air resistance is negligible, which statement best applies?
    1. Both objects hit the ground together.
    2. The greater mass hits the ground first.
    3. The smaller mass hits the ground first.
    4. No conclusion can be made with the information given.
  3. Norma releases a bowling ball from rest; it rolls down a ramp with constant acceleration. After half a second it has traveled 0.5 m. How far has it traveled after two seconds?
    1. 1 m           C. 4 m
    2. 2 m           D. 8 m
  4. The value of an object's acceleration may be characterized in equivalent words by which of the following?
    1. displacement                                     C. velocity
    2. rate of change of displacement         D. rate oc change of velocity
  5. In the case of constant acceleration, the average velocity equals the instantaneous velocity
    1. at the beginning of the time interval
    2. at the end of the time interval
    3. half-way through the time interval
    4. three-fourths of the way through the time interval
  6. A student adds two vectors with magnitudes of 10 and 3. The magnitude of the resultant is definitely one of the following. Which one must it be?
    1. 3             C. 10 m
    2. 6             D. 30 m
  7. Acceleration due to gravity on the Moon's surface is 1/6th that on Earth. An astronaut's life support backpack weighs 300 lb on Earth. What does it weigh on the Moon?
    1. 50 lb             C. 300 lb
    2. 135 lb           D. 1 800 lb
  8. A jogger runs halfway around a circular path with a radius of 50 m. What is the magnitude of his displacement?
    1. 50 m               C. 314 m
    2. 100 m             D. 0 m
  9. In the terminology a 500-N block, the 500-N refers to the block's
    1. weight             C. mass
    2. force             D. none of the above
  10. An automobile of mass 2 000 kg moving at 50 m/s is braked suddenly with a constant braking force of 10 000 N. How long does it take the car to stop?
    1. 1 s             C. 5 s
    2. 2 s             D. 10 s
Question #      1            2           3            4            5            6            7            8            9           10     
Your answer          


II.
A ball, released from rest, rolls down ramp A, then along the floor, then up ramp B, as drawn here. Rounded segments at the bottoms of the ramps allow the ball to roll smoothly from a ramp to the floor and vice versa. Air resistance is negligible.

A. Sketch the ball's velocity vs. time and acceleration vs. time, from the moment it's released until the moment it reaches its peak on the second ramp. The positive direction is down the ramp A, to the right along the floor, and up the ramp B. Label your graphs in such a way that we can tell when the ball is on ramp A, when it's on the floor, and when it's on ramp B. Remember to end your graphs at the moment the ball reaches its highest point on ramp B.

B. Now sketch distance vs. time. ("Distance" here means the distance the ball has rolled along the track from its starting place.) Explain your reasoning in words.


















III.
Superguy (S.G.) is flying at the height of the Eiffel tower E near Paris when he sees the Eiffel Tower elevator start to fall (the cable snapped). His x ray vision tells him Lois LaTour is inside.

  1. If Superguy is 1.00 km away from the base of the tower, and the elevator falls from a height of 250 m, how long does Superguy have to save Lois?


  2. If he flies on a straight line path and at constant acceleration a, and reaches Lois just before the elevator crashes at the base, what must be his acceleration?


  3. Check your answer to B. (the acceleration a) in the following crafty way: argue that superguy's vertical acceleration must match that of Lois (give a good reason, "because both are subject to gravity" is not good enough, since superguy can of course fly at any acceleration he chooses), and use geometry of the figure.