Question

question from laws of motion class 11 (JEE)

Answer 1

4N because F=ma

=4* (v-u/t)

=4*(5-2/3)

=4*9(3/3)

=4*1=4N

Answer 2

Given

mass of the body = 4 kg

Distance 's₁' covered in time t = 1 second = 5 m

Distance 's₂' covered in time t third second = 2 m

Hence time taken to cover s₂ =3 -1 = 2 second

Now from equation of motion we have

s = ut+(1/2)at²

Now when the body covers a distance of 5 m its initial velocity will be 0 m/s as the body starts from rest. Thus

s₁ = (1/2)a₁t₁²

a₁ = 2 (s₁ /t₁²) = 10 m/s².

Now also we know

acceleration a₁ = (v - u)/t₁ ; here v= final velocity

v = 10 m/s {as u = 0 and t₁ = 1 s}

Again solving for s₂ = 2 m

s₂ = ut+(1/2)a₂t₂²

Here u = v = 10 m/s

{2(2 - 20)}/4 = a₂

a₂ = - 9 m/s²

We have,

Force = mass × acceleration

= 4 (a₁ + a₂)

= 4 (10 -9)  

Force = 4 N