Question

A car moving along a straight line at a speed of 72km per hr stops in 5s after the brakes are applied. Find the acceleration

Answer 1

convert 72 km/hr to m/s ..multiply by 5/18 to get 20 m/s.
thus, initial velocity=20 m/s...final velocity=0,the time it comes to stop
time= 5 sec
acceleration = final velocity-initial velocity/time
                =0-20/5
                = -20/5
                =-4 m/s squared

Answer 2

acceleration = change in velocity per second square.

first of all,
changing 72 kilometre per hour into metre per second.
72 x 5 / 18 = 20 metres per second.

change in velocity equals 0 - 20
time taken to change is 5 seconds.

acceleration = 0 - 20 / 5
acceleration = -20 / 5
acceleration = -4 m/s².

retardation = 4 metre per second square.
while,
the acceleration = - 4 m/s².

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