The following test consists of two parts. Part I contains 10 multiple choice problems worth 3 points each. Circle the letter of the best answer. Part II contains 3 problems worth a total of 70 points.
To receive full credit on the problems, all reasoning must be shown and your answer must have the appropriate units. There is no partial credit for the multiple choice.
Start by writing down basic definitions or equations that you are using in your solution.
Keep numbers out of your equations until as late as possible in your solutions.
Be careful, be concise, but be complete.
Ask if you don’t understand the statement of a given problem.
You have 50 minutes to complete this exam. Budget your time accordingly!
Part I: Multiple Choice
Circle the letter of the best answer. (3 points each)
1. An object traveling with a constant speed must have zero acceleration.
a. True b. False
You hit a baseball with an initial speed of 12 m/s at an angle which is 24 o above the horizontal. Take the initial point to be the instant after the ball is hit, and the final point to be the instant the ball reaches its highest point. (Take the positive y-direction to be upward.)
2. What is the ball’s initial y-component of velocity?
a. 0 m/s b. 0.41 m/s c. 11 m/s d. 4.9 m/s e. – 9.8 m/s2
3. What is the ball’s final y-component of velocity?
a. 0 m/s b. 0.41 m/s c. 11 m/s d. 4.9 m/s e. – 9.8 m/s2
4. What is the ball’s final x-component of velocity?
a. 0 m/s b. 0.41 m/s c. 11 m/s d. 4.9 m/s e. – 9.8 m/s2
5. What is the ball’s final y-component of acceleration?
a. 0 m/s b. 0.41 m/s c. 11 m/s d. 4.9 m/s e. – 9.8 m/s2
An object of mass 350 g is moving with a velocity in the positive x-direction of 2.5 m/s . A constant force then starts to act on the object so that it acquires an acceleration in the positive y-direction of 0.57 m/s2.
6. What can you say about the force acting on the object?
a. It is zero since the velocity was initially constant.
b. The force is 200 N (+y direction)
c. The force is 200 N (+x direction)
d. The force is 0.20 N (+x direction)
e. The force is 0.20 N (+y direction)
7. What is the x-component of velocity 2.3 s after the force started to act? (Be careful!)
a. 0 m/s b. 2.5 m/s (+x direction) c. 0.57 m/s (+y direction) d. 1.3 m/s (+y direction) e. 3.8 m/s (+y direction)
8. The Fractional Uncertainty of a speed measured in lab is estimated to be 0.05 . The value of the speed that you obtained was 7.5 m/s. What is the uncertainty in the speed measurement that you obtained?
a. 0 b. 5.7 m/s c. 10 m/s d. 0.4 m/s e. 1.3 m/s
You have just studied a system in lab, and have theoretically determined that the mass, M is related to the period T of the observed circular motion by the equation
Your partner tells you that he plotted a graph of M vs. T, but that he obtained a curved behavior, and can go no further with the study. You tell him that, if he had made the right plot, he would have obtained a linear behavior, and thus could have easily obtained the experimental equation relating M to T.
9. What plot should your partner have made in order to obtain a linear behavior?
a. M vs. T b. M2 vs. T c. M vs. T1/2 d. M2 vs. T1/2 e. M vs. T2
10. What would you expect to obtain for the slope of the graph in question 9?
a. 0 b. 2p/g c. (2p/g)1/2 d. (2p/g)2 e. g/2p
Part II: Problems
Show all work to receive full credit.
1.(25 points) A diver runs horizontally with a speed of 2.3 m/s off of a platform which is 7.4 m above the water’s surface.
a. How long does it take for the diver to hit the water?
b. At what horizontal distance from the point where she left the platform does the diver hit the water?
c. With what speed does the diver hit the water?
2.(25 points) A record of diameter 0.300 m is rotating at a rate of 33.3 rpm (revolutions per minute). You place a penny of mass 4.2 g at the outer edge of the rotating record, and notice that it just barely remains on the record (that is, it just about slides off). Note: In this problem, denote the frictional force by Ff , to avoid confusion with the frequency, f.
a. Draw a rough sketch of the penny on the record, and then draw a good FBD for the penny.
b. What is the period of rotation for the penny?
c. What is the speed of the penny?
d. What is the value of the coefficient of friction between the penny and the record?
e. Is the coefficient in part (d) static or kinetic friction? Explain.
3.(20 points) A block of mass 3.2 kg is sliding up a frictionless incline of angle 22o , as shown in the diagram below. Its speed at the bottom of the incline as it was heading up was 2.5 m/s.
a. Draw a good FBD for the block as it is sliding up the incline.
b. What is the acceleration of the block during its slide?
c. What distance up the incline does the block travel before coming to a stop?
1. b 2. d 3. a 4. c 5. e
6. e 7. b 8. d 9. d 10. b
Part II: Problems
1. (a) 1.2 s (b) 2.8 m (c) 12.3 m/s
2. (a) Sketch (b) 1.79 s (c) 0.53 m/s (d) 0.19 (e) Static; no sliding motion.
3. (a) FBD (b) – 3.67 m/s2 (c) 0.85 m