Question

A body of mass 4kg is accelerated by a constant force travels dist. Of 5m in 1st sec nd 2m in 3rd sec.The force on body is?

Answer 1

Sn = u +a/2(2n-1)
5=u+a/2(2*1-1)
5=u+a/2(1)
5=u+a/2
10=2u+a
10-a= 2u

2= u+a/2(2*3-1)
2=u+a/2(5)
2=u+5a/2
4=2u+5a

putting 2u=10-a
4=10-a+5a
4-10=4a
-6/4=a
-3/2 = a
Force = ma= 4*-3/2=-6N

Answer 2

Distance traveled during the nth sec. Sn = u + (n - 1/2) * a

So S1= u + a /2 = 5
And S3 = u + 5 a/2 = 2

Solving them we get a = -1.5 m/s^2.
m = 4 kg

Force = m a = - 6.0 Newton