Question

A particle of mass 7.5 kg is moving at a steady speed of 12ms-1 when it meets with a constant resistance of 10N. How long does it take to come to rest?

Answer 1

The acceleration of the particle

$$a=\frac{F}{m}=\frac{10\:\rm N}{7.5\:\rm kg}=1.3\:\rm m/s^2.$$

The time of motion to the rest

$$t=\frac{v}{a}=\frac{12\:\rm m/s}{1/3\:\rm m/s^2}=9\:\rm s.$$