Physics 201 exam 3

1. If a planet had twice the radius of the earth, what would it's mass have to be in order to have the same acceleration of gravity (g)?

4 M

2. Two satellites A and B of the same mass are going around the earth in concentric orbits. The distance of satellite B from earths center is twice that of satellite A. What is the ratio of the centripetal force acting on B compared to that acting on satellite A.

1/2

3. A planet of mass m is a distance d from Earth. Another planet of mass 2m is a distance 2d from Earth. Which force vector best represents the direction of total gravitational force on Earth.

2

4. Suppose Earth had no atmosphere and a ball were fired from the top of Mount Everest in a direction tangent to the ground. If the initial speed were high enough to cause the ball to travel in a circular trajectory around the Earth, the ball's acceleration would...

approx equal to g

5. A ball tied to a string is being whirled around in a circle. What can you say about the work done by tension?

tension does no work at all

6. A ball is being pulled up a rough incline by a rope connected to a pulley. How many forces are doing work on the box?

three forces

7. By what factor does the kinetic energy of a car change when its speed is tripled?

9

8. Car #1 has twice the mass of car #2, but they both have the same kinetic energy. How do their speeds compare?

sqrt2v1=v2

9. The work w0 accelerates a car from 0 to 50 km/hr. How much work is needed to accelerate the car from 50 to 150 km/hr

8 wo

10. You and your friend both solve a problem involving a skier going down a slope. The two of you have chosen different levels for y=0 in this problem. Which of the following quantities will you and your friend agree on? A. Skiers PE B. Skier's change in PE C. skiers final KE

only B and C

11. Three balls of equal mass start from rest and roll down different ramps. All ramps have the same height. Which ball has the greater speed at the bottom of its ramp?

same speed of all balls

12. A truck initially at rest , rolls down a frictionless hill and reaches 20 m/s at the bottom. To reach 40 m/s at the bottom, how many times higher must the hill be?

4 times the height

13. Two paths lead to the top of a big hill. One is steep and direct while the other is twice as long and less steep. How much potential energy would you gain if you take the longer path?

the same

14. You see a leaf falling at a constant speed. When you first notice it, the leaf has initial total energy Pei +Kei. You watch the leaf until just before it hits the ground, at which point it has final total energy PEf +KEf. How do these total energies compare?

PEi + KEI >PEf + KEf

15. A mass attached to a vertical spring causes the spring to stretch and the mass move downwards. What can you say about the spring's potential energy (Pes) and the gravitational potential energy (PEg) of the mass.

PEs increases and PEg decreases

A box sliding on a frictionless flat surface runs into a fixed spring, which compresses a distance x to stop the box. If the initial speed of the box was doubled, how much would the spring compress in this case.

twice as much

You throw a ball straight into the air. In addition to gravity, the ball feels a force due to air resistance. Compared to the time it takes the ball to go up, the time it takes to come back down is..

greater

18. Mike applied 10 N of force over 3 m in in 10 seconds. Joe applied the same force over the same distance in 1 min. Who did more work?

same

19. Mike performed 5 J of work in 10 seconds and Joe performed 3J of work in 5 sec. Who produced greather power?

Joe

20. When you pay the electric company by the kilowatt-hour, what are you actually paying for?

energy

21. Which contributes more to the cost of your electric bill each month? A 1500 watt hairdryer or a 600 watt microwave over?

depends on how long each is on

22. An open cart rolls along a frictionless track while it is raining, as it rolls what happens to the speed of the cart as rain collects in it (assume the rain falls vertically into the box)

slows down

23. A net force of 200 N acts on a 100 kg boulder, and a force of the same magnitude acts on a 130 kg pebble. How does the change in the boulders momentum compare to the rate of change of the pebbles momentum?

equal to

24. Two boxes, one heavier than the other are initially at rest on a horizontal frictionless surface. The same constant force F acts on each one for exactly one second. Which box has more momentum after the force acts.

both the same

25. A bowling ball and a ping pong ball are rolling toward you with the same momentum. If you exert the same force to stop each one, for which is the stopping distance greater?

the ping ping ball

26. If all 3 collisions below are totally inelastic which one will bring the car to the left to a complete stop

all three

27. A uranium nucleus at rest undergoes fission and splits into 2 fragments, one heavy and the other one light. Which fragment has the greater momentum magnitude

both have the same

28. On a frictionless surface, a sliding box collides and sticks to a second identical box which is initially at rest. What is the final KE of the system in terms of the initial KE?

KEf = KEi/2

29. If all three collisions below are totally inelastic, which ones will cause the most damage (in terms of lost energy

III

30. Amy (150 lbs) and Gwen (50 lbs) are standing on slippery ice and push each other. If Amy slides at 6 m/s what speed does Gwen have?

18 m/s

31. Consider 2 elastic collisions 1) a golf ball with a speed v hits a stationary bowling ball head on 2) a bowling ball with speed v hits a stationary golf ball head on in which case does the golf ball has the greater speed after the collision?

Situation 2

True or False

more power is required while slowly lifting a box than while quickly lifting a box

False

a source of energy is required to do work

true

true or false

work cannot be done in the absence of motion

true

energy conservation law for projectile (no friction) PE decreases as KE increases

true

w/out friction or work by an external force, the sum of potential and kinetic energies is a constant

true

work is done when the form of energy changes

true