17 , d . because a force is being applied but it is not moving .
19 . is c .
20 .b .
21 . d .
31 . d .
Use the definition of average acceleration:
<em>a</em> = ∆<em>v</em> / <em>t</em>
If <em>v</em> is the starting speed, then ∆<em>v</em> = 0 - <em>v</em>, so solve for <em>v</em> :
-6.42 m/s² = (0 - <em>v</em>) / (2.85 s)
<em>v</em> = (6.42 m/s²) (2.85 s)
<em>v</em> ≈ 18.3 m/s
V = frequency * wavelength
v = 80 * 4
v = 320m/s
<span>The period of a wave can be calculate according T = 1 / f
where T is wave period and f is frequency,
then in our problem we have a wave of 100 Hz so:
T = 1 / 100 = 0.01 seconds
The wave have a period of 0.01 seconds.
Optinaly we could also calculate the speed: V=wavelenght/period= 2/0.01= 200 m/s</span>
Sound is an example of a longitudinal wave.