### Q.6:- A constant force acting on a body of mass 3.0 kg changes its speed from 2.0 m s^{–1} to 3.5 m s^{–1}in 25 s. The direction of the motion of the body remains unchanged. What is the magnitude and direction of the force?

**Answer:-**Mass of the body, *m* = 3 kg

Initial speed of the body, *u* = 2 m/s

Final speed of the body, *v* = 3.5 m/s

Time, *t* = 25 s

Using the first equation of motion, the acceleration (*a*) produced in the body can be calculated as:

*v* = *u + at*

∴ a = (v – u) / t

= (3.5 – 2) / 25 = 0.06 ms^{-2}

As per Newton’s second law of motion, force is given as:

*F* = *ma*

= 3 × 0.06 = 0.18 N

Since the application of force does not change the direction of the body, the net force acting on the body is in the direction of its motion.