Question

A body of mass $4\, kg$ is accelerated upon by a constant force, travels a distance of $5\,m$ in the first second and a distance of $2\,m$ in the third second. The force acting on the body is

• A. 2 N
• B. 4 N
• C. 6 N
• D. 8 N

Answer 1

Answer: (C)

6 N

Answer 2

Distance travelled by the body in $n^{\text {th }}$ second is given by
$S_{n}=u+\frac{a}{2}(2 n-1)$
$5=u+\frac{a}{2}(2 \times 1-1)$
$5=u+\frac{a}{2}\,\,\,\,\,\,\,\,\,\,\,\,...(i)$
$2=u+\frac{a}{2}(2 \times 3-1)$
$2=u+\frac{5}{2} a\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,....(ii)$
Solving Eqs. (i) and (ii), we get
$a=-\frac{6}{4}\, m / s ^{2}$
ie, body is decelerating
mass $=4 \,kg$
and$\,\,\,\,\,F=m \times a=4 \times \frac{6}{4}=6 \,N$