1. As long as the bus is stationary, you have a tendency to remain at rest. As the bus starts up, inertia causes you to remain stationary. When the bus begins to move, you tend to stay in place which corresponds to falling backward in the frame of the moving bus.
3. When a moving vehicle comes to rest or quickly slows, the contents (including passengers) tend to remain in motion. The contents seem to move forward relative to the vehicle, not toward the rear. Based on Newton's First Law the judge would probably decide against the passanger's claim.
16. Less, since your distance from the center of the earth would be greater, and the gravitational force varies as the inverse square of the distance.
28. (a) W = m g = (75.0 kg) x (9.8 m/s2) = 735
N.
(b) W = (75.0 kg) x (8.70 m/s2)
= 653 N.
31. Multiple Choice: A. (a) B.
(c) C. (b) D. (d) E. (c)
F. (b) G. (d) H. (c) I. (d)
J. (c)
Ch. 6:
2. The light body has the greater velocity, since the momentum p = mv is the same for the two bodies.
16. What we know: m = 70.0 kg
h = 5.00 m t = 10.0 s
Equations: power
= work/time P = W/t work = force x
distance F = mg
so:
P = m g h / t = (70 kg) (9.8 m/s2) (5 m) / (10 s) = 343
joules/s = 343 watts
converting to hp:
343 watts x (1 hp / 746 watts) = 0.46 hp.
28. What we know: m = 0.200 kg
v = 15.00 m/s
(a) KE = ½ mv2
= ½ (0.200 kg) (15.0 m/s)2 = 22.5 joules.
(b) double v: KE =
½ (0.200 kg)(30.0 m/s)2 = 90.0 joules
36. What we know: m = 60.0 g = 0.060 kg
vi = 0 m/s h = 100 m
(a) PE = m g h = (0.06 kg) (9.8
m/s2) (100 m) = 58.8 joules
(b) Conservation of energy:
KE (final) = PE (initial),
so ½ mv2 = m g h and v2 = 2 g h = 2
x (9.8 m/s2) x (100 m) = 1960 m2/s2.
Thus, v = 43 m/s Note: the mass
was not needed to find the velocity.
We
could also use the equation h = s = vi t + ½ a
t2 with a = g giving t2 = 2h/g
and v = vi + a t = gt so v2 = g2t2
=
g22h/g = 2 g h as above.
43. Multiple Choice: A. (b) B. (d) C. (b) D. (d) E. (c) F. (b) G. (c) H. (c) I. (d) J. (b)