13. Yes, an automobile traveling a curved
path changes its direction and is therefore accelerating, even if its speed
is constant.
Remember,
acceleration is the rate of change of velocity, and velocity is speed plus
direction. So either a change in speed or a change in velocity (or both)
can cause acceleration.
14. What we know: vi =
22.0 ft/s, a = 4.0 ft/s2,
t = 15.0 s
What we
want to find: the final velocity, v
The equation
we will use: v = vi + a t
v = (22.0 ft/s) + ( 4.0 ft/s2)(15.0
s) = 82.0 ft/s
20. What we know: vi =
0 m/s, a = 2.0 m/s2,
t = 5.0 s
What we
want to find: the final velocity, v
The equation
we will use: v = vi + a t
v = (0 m/s) + (2.0 m/s2)(5.0 s) = 10.0 m/s
22. What we know: freely falling
ball: a = g = 9.8 m/s2, t = 3.00
s, from rest vi = 0 m/s
What we
want to find: the final velocity, v
The equation
we will use: v = vi + a t
v = (0 m/s) + (9.8 m/s2)(3.0 s) = 29.4 m/s
in metric units, or
v = (0 ft/s) + (32 ft/s2)(3.0 s) = 96.0 ft/s
in common units.
31. Multiple Choice: A. (b) B. (c) C. (c) D. (a) E. (c) F. (b) G. (b) H. (c) I. (b) J. (d)
Ch. 4:
1. The Ptolemic system was based on a geocentric model: an immobile earth at the center of a finite universe. This was satisfying to most people and it was in complete harmony with Aristotelian physics.
2. Copernicus’ heliocentric theory of the solar system demoted the earth from its position in the center of the universe to just one body among several circling around the sun. The effect was to lower humanity’s perception of itself and its place in the universe.
10. The exceedingly small angles involved make the method of parallax impractical for very distant stars.
13. Supporters of Ptolemy were firm in their belief that the perfect circle was the appropriate path for the motion of heavenly bodies. Any deviation from a circle, such as an ellipse, was considered objectionable.
20. Multiple Choice: A. (c) B. (b) C. (c) D. (a) E. (d)