**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.**