Question

An object of mass $10 \,kg$ moves at a constant speed of $10\, m/s$. A constant force, that acts for $4 \,s$ on the object, gives it a speed $2\, m/s$ in opposite direction. The force acting on the object is

• A. -3 N
• B. -30 N
• C. 3 N
• D. 30 N

Answer 1

Answer: (B)

From first equation of motion,
$v =u+a t $
$ v-u =a t, \,\, a=\frac{v-u}{t} $
Given $: u=10 \,m/s , v = -2\, m/s , t = 4 s $
$ a =-\frac{-2-10}{4}=-3 \,m / s ^{2} $
So, force acting on the object
$F= ma=10 \times(-3)=-30\, N$