Question

For how long should a force of 100 n act on a body:of mass 20kg so that it acquires a velocity of 100 m/s ?

Answer 1

So acceleration of the body can be calculated as:

F = ma

F = 100 N and m = 20 kg

a = 100/20 = 5 m/s2

Since, the force is acting constantly over the body, the acceleration is uniform; the equations of motion can be applied:

v = u + at

Where v = 100 m/sec, a = 5 m/s2 and u = 0 (rest).

t = v/a = 100/5 = 20

Answer 2

Force (F) = 100 N.
Mass (m) = 20 kg.
Final velocity = 100m/s.
Initial velocity = 0 m/s [considering that the object starts from rest].
Time = t.

$f = \frac{m(v - u)}{t} \\ 100 = \frac{20 \times (100 - 0)}{t} \\ 100 = \frac{20 \times 100}{t} \\ 100 = \frac{2000}{t} \\ t = \frac{2000}{100} \\ t = 20 \: s.$
Therefore, a force of mass 100 N acting on a body of mass 20 kg to attain a velocity of 100 m/s takes 20 seconds.