PHYS 141 Fall 2018 Final Exam You will be graded on your communication of physics to me. It is more important to set a problem up than get the final answer. Therefore, please make sure you set up all problems rather than finish some of the problems and leave some blank

1. A spring of spring constant 2500 N/m is compressed 10 cm behind a 250 g projectile. When released, the projectile is fired into and sticks inside of a 2.0 kg block. The block and projectile lift up to a maximum height dh. Clearly Explaining your work, find the expected elevation gain, dh….. I find the following embodiment better for this problem because it is more thoughtful: I have a plan to use Usp = Ug to solve for the final height. Does this method work? - If this the correct way to find dh, please explain

why this is correct, and find dh. - If this method doesn’t work, please explain why it will not work and what has to be done differently to find dh.

You don’t have to calculate it.

dh

2. An asteroid is initially motionless next to me with v = 0, and 𝜔 0. Then, a cannon ball is fired from the surface of the asteroid out into space as shown.

a) After the cannonball is fired, is the asteroid still motionless? with a drawing describe the asteroid’s subsequent motion with directions and support your statements with physics concepts.

…did you remember to indicate direction(s)?

b) In the above problem, please quantify the asteroid’s subsequent motion. The asteroid is a 1000 kg

solid sphere of radius 2 m, and the 5 kg cannon ball is fired at a speed of 100 m/s. Describe how you would find the actual values of the subsequent motion. Set up the equations, but you don’t have to substitute numbers or solve them.

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3. Two carts, A and B, are initially at rest on a frictionless, horizontal table. A constant force of magnitude Fo is exerted on each cart as it travels from the first mark on the table to the second, after which each cart glides freely. The mass of cart B is greater than that of cart A.

a) Is the magnitude of the acceleration of cart A greater than, less than, or equal to the magnitude

of the acceleration of car cart B while the carts are between the two marks? Explain. b) Is the kinetic energy of cart A great than, less than, or equal to the kinetic energy of cart B after

the carts have passed the second mark? Explain. c) Is the magnitude of the momentum of cart A greater than, less than, or equal to the magnitude

of the momentum of cart B after the carts have passed the second marks? Explain.

4. You and your friend Sara have the exact same yo-yo, seen at right. You are both given 12 quarters to paste onto the outside of your yo-yo (6 quarters on each side). You glue your quarters near the outside of the rim, while Sarah glues her quarters on top of each other at the center of the yo-yo. We let both yo-yos fall, measuring the tension in the string as they fall. Which yo-yo has a string with greater tension or are they the same tension? Support your answer with a complete discussion.

Sarah’s Yours

5. I shoot a 1 kg ball off the edge of a 100 m high cliff at a speed of 40 m/s at an angle of 60 above the horizon. Find the answers in any order.

a) Find the speed of the ball when it hits the ground 100 m below. b) Find the angle that the ball’s velocity makes with the horizontal when it hits the ground

a) v = ______ b) theta = ______

6. A car drives in a horizontal, circular path of radius 40 m. The very slippery road is banked at a high angle as shown. Find in either order:

a) The correct speed for the car to execute the turn. b) The reading of the scale under my 70 kg body while I execute the turn at the correct speed.

v = _______ reading on scale = _______

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40 m to center of circular road

7. On a perfectly spherical planet, you stand on a spring scale at the pole, about which the planet is spinning. Then you go to the equator and do the same measurement. Compared to the measurement at the pole, will the spring scale at the equator indicate the same force, greater force or smaller force? Make your argument clear to convince someone who doesn’t agree with you.

8. At right, a solid disk is spinning in the air such that the edge closer to you is moving downward. The right end of the axel is resting on a pedestal while the left side of the axel is unsupported.

a) Label the diagram at right, clearly showing direction: i) All forces on the disk/axel assembly. ii) The angular momentum of the spinning disc. iii) Any torque on the disc/axel assembly.

b) Please describe the motion of the spinning disk as explained above with only the right side of the axel resting on the pedestal. With good illustrations, explain how you got this answer.

X

9. You witness a collision on a slippery road. A 1000 kg car moving at 40 m/s West hits a stationary 5000 kg truck and bounces off at 30 m/s North at a right angle as shown. Find the velocity of the truck after the collision, including the direction (angle).

car Truck Vo=0

N car

10. A 100 kg uniform bar is secured by a rotating pivot and cable as shown. Please find the tension in the cable and the force provided by the pivot. You may use trigonometry or graphic approximation as you choose.

Tension = ___________________________________ (include direction) FP= ________________________________________ (include direction) What’s Your Name?________________________________________________________

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3 m1 m

4 m