Homework set 2

1. A cheetah can travel at 60 mph top speed.  What is its speed in meters per second?
A: 26.7    (Correct)
B: 30
C: 135
D: 45

2. A space shuttle astronaut on liftoff will occasionally experience accelerations equal to 3 g's
because of the rocket engines' thrust.  What is this acceleration in meters per second per second?
A: 3.0
B: 29.4    (Correct)
C: 15.2
D  9.5

3. A person jumps from a plane and begins free fall, accelerating at a rate of 9.8 m/s^2.  How fast
will that person be moving after three seconds?
A: 9.8 m/s
B: 19.6 m/s
C: 3.0 m/s
D: 29.4 m/s (correct)

4. A train travels 1300 miles in 10 hours.  What was its velocity?
A: 13 mph
B: 2 m/s
C: 130 mph   (Correct)
D: 200 mph

5. Which of Newton's laws best explains how rockets can fly in empty space?
A: 1st Law (law of inertia)
B: 2nd Law (F = ma)
C: 3rd Law (Action/Reaction)    (Correct)
D: The conservation of energy

6. Which of Newton's laws best explains why it's harder to push a broken down Lexus (in neutral)
than a broken down VW?
A: 1st Law (law of inertia)
B: 2nd Law (F = ma)    (Correct)
C: 3rd Law (Action/Reaction)
D: The conservation of energy

7. Which of Newton's laws best explains why in order for something to move in a circle, there
must be a force pulling it into the center of the circle (like gravity, which pulls satellites toward
the center of the earth)?
A: 1st Law (law of inertia)    (Correct)
B: 2nd Law (F = ma)
C: 3rd Law (Action/Reaction)
D: The conservation of energy

8. Which object can do more work?
A: A 100 kg rock sitting on the floor.
B: A 100 kg rock rolling on the floor at v = 1 m/s.
C: A 100 kg rock sitting on the ledge of a 10 m high building?     (Correct)
D: none of the above.

9. How much energy would it take to lift a 1000 kg car 2 meters off the ground?
A: 19,600 J    (Correct)
B: 500 J
C: 2,000 J
D: 4,900 J

10. A counter weight used for operating a draw bridge has a mass of 10,000 kg.  What is the
maximum work it can do if the maximum height to which it can be raised is 5 m?
A: 490,000 Joules     (Correct)
B: 50,000 Joules
C: 10,000 Joules
D: not enough information