Question

A cameraman on a pickup truck is traveling westward at 23 km/h while he videotapes a cheetah that is moving westward 23 km/h faster than the truck. Suddenly, the cheetah stops, turns, and then run at 48 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 2.2 s. What are the (a) magnitude and (b) direction of the animal’s acceleration according to the cameraman and the (c) magnitude and (d) direction according to the nervous crew member?

Answer 1

(a) and (b)

Intital velocity of the cheetah as observed by the cameraman : 23 km / h westward.

Final velocity of the cheetah as observed by the cameraman : ( 48 + 23 ) km / h westward = 71 km / h eastward.

Hence, according to the cameraman. change in velocity of the cheetah is :

( 71 + 23 ) km / h = 94 km / h = ( 94000 / 3600 ) m / s = 26.11 m /s towards east.

Hence, according to the cameraman. acceleration of the cheetah is :

( 26.11 / 2.2 ) m / s² = 11.87 m / s² eastward.

(c) and (d)

Intital velocity of the cheetah as observed by the crew member : ( 23 + 23 ) km / h = 46 km / h westward.

Final velocity of the cheetah as observed by the crew member : ( 48 + 46 ) km / h westward = 94 km / h eastward.

Hence, according to the crew member. change in velocity of the cheetah is :

( 94 + 46 ) km / h = 140 km / h = ( 140000 / 3600 ) m / s = 38.89 m /s towards east.

Hence, according to the crew member. acceleration of the cheetah is :

( 38.89 / 2.2 ) m / s² = 17.7 m / s² eastward.