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Exam 1, Sample Physics 172H fall 2007 Purdue University Print your name__________________________________________ Lab section_______ Do not use other paper. Write on the back of this test if needed. All problems except the last one are multiple-choice and only the correct answer is graded. For the last problem only you must provide the complete reasoning and solution as requested in the problem:
- Correct answers without adequate explanations or with incorrect reasoning will be counted wrong. Cross out anything you don’t want us to read.
- Make explanations complete, but brief. Do not write a lot of prose.
- Include diagrams where appropriate to explain your work.
- Show what goes into a calculation, not just the final number: (2m)/(4 s) = 0.5 m/s
- Give standard SI units with your results
- Unless specifically asked to derive a result, you may start from the formulae given on the equation sheet. All equations used must be derived from those on the equation sheet.
- Use correct vector notation
- Your work must be legible and clear
Problem 1. The x coordinate of the position of a mouse as a function of time is plotted below. If each square on the grid is 1 [s] in time and 1 [m] in length, what is the average velocity vx of the mouse during the 12 seconds shown? a. 1 [m/s] b. –1 [m/s] c. 0.083 [m/s] d. –0.083 [m/s] e. 0 [m/s] Problem 2 A pool ball of mass 0.10 kg, hits a side of the pool table with a velocity of <3, 0, 1.5> [m/s]. It rebounds with a velocity of <3, 0, -1.5> [m/s]. If the time of contact between the ball and the pool table wall is 0.03 [s], calculate the force of impact that the ball delivers to the pool table. a. <0, 0, 3> [N] b. <0, 0, -3> [N] c. <0, 0, 10> [N] d. <0, 0, -10> [N] e. <3, 0, 3> [N] f. <3, 0, -3> [N] g. <-6, 0, 10> [N] h. <-6, 0, -10> [N]
t
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Problem 7. For the following speeds determine whether or not it is valid to approximate gamma as 1. I. A proton zips by at 2.934E7 m/s. II. A cosmic ray flies by at 2.9E7 m/s III. You ride your bike to school at 10 m/s a. I and II only b. I and III only c. I, II and III d. II and III only e. I only f. II only g. III only Problem 8 – 9. The position and momentum of a bee is displayed by the vectors in the graph below. Problem 8. What is the significance of the location of the tip of the momentum vector on the graph (<-2, 4, 0>[m])? a. It is where the bee is. b. It is where the bee will be at a later time. c. It has no significance on the position graph. d. It is where the bee was at an earlier time.
X
Y
Problem 9 What is the significance of the location of the tip of the position vector on the graph (<3, 3, 0>[m])? a. It is where the bee is. b. It is where the bee will be at a later time. c. It has no significance on the position graph. It is where the bee was at an earlier time. Problem 10 - 12. Problem 10. Which vectors are equal to
r? a.
a e.
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b i.
c ,
d b.
b f.
a ,
c j.
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d c.
c g.
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d h.
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d Problem 11. Which vectors have the same magnitude as
r? a.
a e.
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b i.
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d b.
b f.
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c j.
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d c.
c g.
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Problem 15. For the following situations state whether an interaction occurred. I. A runner speeds up on a straight track. II. A spaceship travels at constant velocity in deep space. III. A ballon floats stationary in the air. b. I only c. II only d. III only e. I and II only f. I, II and III g. I and III only h. II and III only Problem 16 – 17. Remarkable data indicate the presence of a massive black hole at the center of our Milky Way galaxy. The star nearest the center of our galaxy was observed to be about 1E14 m from the center, with a period of about 15 years. Assume the orbit is circular. Problem 16. What is the value of gamma for this speed? a. 1. b. 1. c. 1. d. 1. e. 1. f. 1. Problem 17. What is the mass of the black hole? a. 2.6E36 kg b. 3.2E37 kg c. 4.0E32 kg d. 2.2E34 kg e. 2.4E35 kg f. 3.2E36 kg
Problem 18. A spring has a relaxed length of 1.5 m and spring constant 300 N/m. You attach a mass of 0.4 kg to one end of the spring, and then swing the ball around your head in a circle, causing the spring to stretch to a new length of 1.8 m. What is the speed of the ball? a. 36.7 m/s b. 405 m/s c. 161 m/s d. 12.7 m/s e. 20.1 m/s f. 14.0 m/s Problem 19. Two cannon balls are dropped together from the top of the Leaning Tower of Pisa. One has mass M, the other has mass 4M. Ignore the effects of air on these two objects. Choose the correct statement: a. The two balls experience equal forces, and hit the ground at the same time. b. The two balls had equal changes in velocity, and hit the ground at the same time. c. The two balls had equal changes in momenta, and hit the ground at the same time. d. None of the above. Problem 20. A 500 kg car with velocity <20, 0, 0> [m/s] is traveling east on SR 26 and collides into a 900 kg truck with velocity <0, 0, 5.0> [m/s] that is traveling south on 9th^ street in Lafayette. If the two cars stick together because of the impact, what is their final velocity right after the collision? a. <20, 0, 5.0> [m/s] b. <7.1, 0, 2.9> [m/s] c. <2.4, 0, 7.7> [m/s] d. <3.3, 0, 2.1> [m/s]
c. How would these results change if you pull to the left on the left block (mass m 3 ) with the same force, instead of pushing the right block?
