# 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?

(a) 0.75 s

(b) 1.33 s

(c) 6 s

(d) 35 s

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Acceleration a = $\frac{-F}{m}$ = $\frac{50}{20}$ = -2.5 ms-2

u = 15 ms-1

V = 0

t = ?

v = u + at

0 = 15 – 2.5t

t = $\frac{15}{2.5}$ =6s