1. inertia
2. terminal velocity
3. Projectile motion
4. Momentum
5. Free fall
6. B
7. D
8. D
9. B
10. B
11. Accept all reasonable answers. Sample
answers: A feather falling inside a vacuum
chamber is in free fall. An object dropped on
the moon is in free fall.
12. Gravity and air resistance combine to give a
net force on a falling object. When gravity
and air resistance are the same size but in
opposite directions, the object stops
accelerating downward and has reached its
terminal velocity.
13. Friction is a force that opposes the motion of
objects. Friction slows the motion of moving
objects so you don’t see objects moving
forever in a straight line.
14. a. Δυ = g
x
t = 9.8 m/s
2
x 1.5 s = 14.7 m/s
b. p=5 m x v 5 12 kg x 14.7 m/s = 176.4
kg•m/s
16. Newton’s second law: a = F/m. During
takeoff, the shuttle burns fuel and therefore
loses mass. However, the forward force on
the shuttle remains the same. So, the
shuttle’s acceleration increases because its
mass constantly decreases during takeoff.
17. When the hammer hits the nail, the hammer
stops. Its momentum is transferred to the
nail, driving it into the wood. Momentum is
also transferred from the hammer to your
hand and from the nail to the wood and to
the work bench or table top.
18. You will move away from your friend (in
the direction opposite from where you threw
the backpack). The action force is you
pushing the backpack toward your friend.
The reaction force is the backpack pushing
you away from your friend.
19. The law of conservation of momentum:
when two or more objects interact, the total
amount of momentum must stay the same.
The ball moving in the air has a certain
amount of momentum, and the balls at rest
have no momentum. When the moving ball
hits the balls at rest, all of its momentum is
transferred to them, and it comes to a stop.
The momentum is transferred from ball to
ball until it reaches the ball on the other end.
The ball on the other end keeps all the
momentum, and it moves away from the
other balls.
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