A cameraman on a pickup truck is traveling westward at 16 km/h while he videotap

Question

A cameraman on a pickup truck is traveling westward at 16 km/h while he videotapes a cheetah that is moving westward 31 km/h faster than the truck. Suddenly, the cheetah stops, turns, and then runs at 45 km/h eastward, as measured by a suddenly nervous crew member who stands alongside the cheetah's path. The change in the animal's velocity takes 2.2s. (Use east as the positive direction.)

(a) What is its acceleration from the perspective of the cameraman?
m/s2

(b) What is its acceleration from the perspective of the nervous crew member?
m/s2

Explanation / Answer

with respect to cameraman

initial velocity of cheetah is u = 31-16 = 15 km/hr = 15*(5/18) = 4.2 m/sec

final velocity is v = 45+16 = 61 km/hr = 16.94 m/sec

time taken is 2.2 sec

a) a = (16.94-4.2)/2.2 = 5.8 m/s^2

b) accelaration a = (v-u)/t

v = 45*5/18 = 12.5 m/sec

u = 31*5/18 =8.62 m/sec

t = 2.2 sec

a = (12.5-8.62)/2.2 = 1.76 m/s^2

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