A body of mass 2 kg travels according to the law x(t)=pt+qt²+rt³,where p=3 m/s,q=4 m/s² and r=5 m/s³.The force acting on the body at t=2 s is

Options

(a) 136 N
(b) 134 N
(c) 158 N
(d) 68 N

Correct Answer:

136 N

Explanation:

m = 2 kg, x = pt + qt² + rt³
⇒ dx/dt = p + 2qt + 3rt²
d²x/dt² = 2q + 6rt = acceleration(a)
At t=2s,
a = 2q +12r = 2 x 4 + 12 x 5
= 68 m/s²
F=ma = 2 x 68 = 136 N.