# What force must be applied to a body with a mass of m = 90 kg, lying on a smooth horizontal

**What force must be applied to a body with a mass of m = 90 kg, lying on a smooth horizontal surface, so that it gains a speed of v = 8m / s in 4 seconds.**

Given:

m = 90 kilograms is the mass of a body lying on a smooth horizontal surface;

v = 8 meters per second – required body speed;

t = 4 seconds – the interval during which the body must acquire the speed v.

It is required to determine F (Newton) – what force must be applied to the body.

By the condition of the problem, we do not take the friction force into account.

Let’s find the acceleration that the body should have:

a = v / t = 8/4 = 2 meters per second squared.

Then, to determine the force, it is necessary to use the following formula (Newton’s second law):

F = m * a;

F = 90 * 2;

F = 180 Newton.

Answer: a force equal to 180 Newtons must be applied to the body.