Physics 111
Test #2 Formula Sheet
Physics 111 – Test 2
9 June 2015
Name______
Directions: This is a CLOSED BOOK test, and you may only use the calculator and cheat sheet provided. SHOW ALL OF YOUR REASONING! You can only get partial credit for an incorrect answer if you show your reasoning. You may have as much time as you like to finish this exam.
- Speed vs. velocity!
a)(8 pts) Is it possible for something to have a constant velocity but have a non-zero acceleration? If so, give an example. If not, say why not.
b)(8 pts) Is it possible for something to have a constant speed but have a non-zero acceleration? If so, give an example. If not, say why not.
2. (9 pts) Sylvia (mass with equipment = 180 kg) is doing a “space walk.” She is floating in space at rest far from any sources of gravity. Her colleague, Horatio (mass with equipment = also 180 kg), is also at rest. Sylvia throws her battery pack in the +x direction. Does Horatio then see Sylvia move? If so, in what direction does she move? If not, why doesn’t she move?
3. (17pts) A guided missile of mass 500 kg has 4 thrusters that can give it forces in the ±x and ±y directions. The maximum thrust of each thruster is 5.0 × 105 N. The missile is at the origin going 800 m/s in the +x direction. The target you want it to hit is at (x, y) = (500m, 500m). Which thrusters do you turn on and what (constant) forces do you give each in order for the missile to hit the target? (Careful! What happens if you apply the maximum thrust in the +y direction and no thrust in either x direction? Also, note that there is more than one correct answer to this question.)
4. (17 pts) A mass m hangs from two ropes attached to the ceiling as shown in the diagram. The maximum tension any one of the two ropes can handle is 5000 N. What is the maximum m can be so that neither of the two ropes break? (HINT: First determine which rope will have the bigger tension.)
5. (25 pts) Consider the situation illustrated below. What is the maximum mass mC can be so that mA does not slide off of mB? The string has negligible mass, and the pulley has negligible mass and friction. YOU NEED ONLY TO CORRECTLY SET UP THE EQUATIONS YOU WOULD NEED. YOU DO NOT NEED TO SOLVE THEM FOR mc.
mA = 3 kg
mB = 12 kg
6. (16 pts) Our intrepid astronaut Sylvia journeys to the planet Newtonia, where the acceleration of gravity (the value of g) is 15.0 m/s2. The planet’s capital city, Isaacton, has an amusement park. On one ride, Sylvia stands against the inner wall of a hollow vertical cylinder with radius 3.5 m. The cylinder starts to rotate, and when it reaches a constant rotation rate of 0.85 rev/s, the floor on which she stands drops about 6 m. She remains pinned against the wall. What minimum coefficient of static friction is required if she is not to slide downward to the new position of the floor?
BONUS BRAIN BUSTER!!! (+ 5 pts)
Consider a universe where YOU can choose the power of r in the formula for the force of gravity. In other words, this force is equal to , where n is some number. Determine the value of n so that every planet orbiting a star (with a circular orbit) would take the same amount of time to go around it regardless of the radius of the orbit. (Everything goes around in lock step like a turntable.) In other words, every planet’s “year” would be the same length of time. NOTE: The length of this year would still depend on the mass of the star.
Credit will only be given for correct reasoning. If you are able to guess the correct answer but give no correct reasoning, you will receive no extra credit. However, if you give some correct reasoning that would (or does) lead to the correct answer, at least some credit will be given.
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By signing my name above, I affirm that this test represents my work only, without aid from outside sources. In all aspects of this course I perform with honor and integrity.