Kinematics: Motion in One Dimension

self check Constant Velocity Self-Check

Now, you try. Complete the self-check activity by looking at the questions below, working them out, and then clicking on the question to review the explanation.

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A bird can fly 25 km/h. How long does it take to fly 15 km?
Given:
v = 25 km/h
d = 15 km
Find:
time, t = ?		 Equations:
v equals d over delta t
Solution:
v equals d over delta t; twenty five kilometers per hour equals fifteen kilometers over delta t; delta t equals fifteen kilometers over twenty five kilometers per hour equals point six hours

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According to a rule-of-thumb, every five seconds between a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.
Given:
t = 5 s
d = 1 mi
Find:
speed, vsound		 Equations:
v equals d over delta t
Solution:
v equals one mile over 5 seconds times 1600 meters over one mile equals 320 meters per second

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A person jogs eight complete laps around a quarter-mile track in a total time of 12.5 minutes. Calculate (a) the average speed and (b) the average velocity in m/s.
Given:
d equals four hundred meters times eight equals 3200 meters; delta x equals zero meters; t equals twelve point five min times 60 seconds over 1 min equals 750 seconds
Find:
average speed and velocity, v		 Equations:
v equals d over delta t and v equals delta x over delta t
Solution:
(a)
v equals d over delta t equals 3200 meters over 750 seconds equals 4.3 meters per second

(b)
v equals delta x over delta t equals 0 meters over 750 seconds equals zero point zero meters per second