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Question
A car of mass 480 kg moving at a speed of 54 km h-1 is stopped by applying brakes in 10 s . Calculate the force applied by the brakes .
Solution
Mass, m = 480 kg.
Initial velocity, u = 54 km/hr = 15 m/s.
Final velocity, v = 0.
Time, t = 10 s.
Acceleration = Change in velocity/time.
Or, a = (v - u)/t.
Or, a = (0 - 15)/10 = -1.5 ms-2.
Here, negative sign indicates retardation.
Now, Force = Mass × Acceleration
Or, F = (480) (1.5) = 720 N.
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