# A constant retarding force of 50 N is applied to a body of mass 20 kg moving initially with a speed of 15 m/s.

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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 m/s. How long does the body takes to stop?

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Given; u = 15m/s; v = 0; t = ?
F = 50N, m = 20kg
∴ Retardation,
a = $\frac{F}{m}=\frac{50}{m}=\frac{50}{20}$ = 2.5 ms-2
Now applying the equation, v = u + at
0 = 15 – 2.5t ⇒ 2.5t = 15
∴ t = $\frac{15}{2.5}$ = 6 sec
or t = 6 sec