A cameraman on a pickup truck is traveling westward at 18 km/h while he videotap

Question

A cameraman on a pickup truck is traveling westward at 18 km/h while he videotapes a cheetah that is moving westward 32 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 1.6 s. (Use east as the positive direction.)

(a) What is its acceleration from the prespective of the cameraman?

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

Explanation / Answer

The velocity of the truck vt = -22km/h = -6.11m/s the velocity of the cheetah vc = 51km/h = - 14.16 m/s the return velocity of the cheetah vr = 45km/h = 12.5 m/s the change in the velocity takes place in time t = 1.7s The relative velocity of the cheetah vi = -14.6-(-6.11) = - 8.49m/s the relative velocity in the return vf = 12.5 + 6.11 = 18.61 m/s therefore the acceleration a = vf -vi / t                                            = 18.61 -(- 8.49) /1.7                                            = 15.94 m/s^2 (b) For the perspective of the nervous crew member          vi = -14.16 and   vf = 12.5 m/s therefore the acceleartion                       a = 12.5 - (-14.16) / 1.7                          = 15.68 m/s^2

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