# Q5.6 A constant force acting on a body of mass 3.0 kg changes its speed from $2.0 ms^{-1}$ to $3.5 ms^{-1}$ in 25 s. The direction of the motion of the body remains unchanged. What is the magnitude and direction of the force?

D Devendra Khairwa

Since the velocity of the body is increased by applying the force. This is possible only when the force is applied in the direction of the motion.

For finding the magnitude of the force, we need to calculate acceleration.

By using first equation of the motion,

$v\ =\ u\ +\ at$

or                                                  $3.5\ =\ 2\ +\ a(25)$

or                                                    $a\ =\ \frac{3.5-2}{25}\ =\ 0.06\ m/s^2$

Thus force can be written as :

$F\ =\ ma$

$=\ 3\times 0.06$

$=\ 0.18\ N$

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