A block is kept on a rough horizontal surface. A variable horizontal force is acting on the block as shown in the figure. At `t=0`, block is at rest. Kinectic energy of block at `t=5 sec` will be `(g=10m//s^(2))`

Options

A. 60 J
B. 160 J
C. 80 J
D. zero

Answer

C

Explanation

`(f_(s))_(max) = 30 N,f_(x) = 20 N` block will start moving at `t=3 sec` after `3 sec` by `F_("net") = ma`
`rArr 10 t - 20 = 10 a rArr a =t -2`
`underset(0)overset(v)(int) dv = underset(3)overset(5)(int) (t-3)dt=v=4 m//s`
`rArr K.E = (1)/(2) xx 10 xx 4_(2) = 80 J`