Question

A body of mass 4 kg is moving on a horizontal surface with an initial velocity of 6 ms-1 comes to rest after 3 sec. If one wants to keep the body moving on the same surface with the velocity of 6 ms-1, the force required is :

Answer 1

F = ma

F=m(v-u/t)

F=m(6-0/3)

F=m(6/3)

F=m(2)

F=(4)(2)

F=8N

Answer 2

Given:

mass = 4kg

initial velocity = 6 m/s

t = 3 sec

To Find:

Force required

Solution:

we know,

F =  ma

also,

v  = u +  at      {1st equation of motion}

⇒ a = (v - u) / t

now,

F = m (v - u) / t

⇒ F = m(6 - 0) / 3       {u=0 since after 3 sec the object comes to rest.}

⇒ F = m(6/3)

⇒ F = 4 * 2 = 8 N

So, force required is 8N.