# A constant retarding force of 50 N is applied to a body of mass 20 kg moving initially with a speed of 15 ms^-1.

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A constant retarding force of 50 N is applied to a body of mass 20 kg moving initially with a speed of 15 ms-1. How long does the body take to stop?

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Given: m = 20 kg, u = 15ms-1, v = 0,

F = – 50 N (retarding force)

To find: Time (t)

Formula: v = u + at

Calculation: Since, F = ma

∴ a = $\frac{F}{m}=\frac{50}{20}$ = -2.5 m s-2

From formula,

0 = 15 + (-2.5) × t

∴ t = 6s

Time taken to stop the body is 6 s.