A block of mass `m = 3kg` resting on a horizontal frictionless flooe is horizontally struck by a 9N force that acts for 0.02 sec. After 3 sec it receivers a second blow of force 9 N but in opposite direction which acts for 0.01 sec. The speed of the body after 30 sec is

Options

A. 0
B. 3 cm/sec
C. 90 cm/sec
D. 30 cm/sec

Answer

B

Explanation

As, impulse received ,
As, `J = 9 xx 0.02 = m (V -0)`
`V = (0.18)/(3) 0.06 m//sec`
Velocity after `3 sec rArr V' = 0.06 m//sec`
Now pulse received by second orce
`J' = -9 xx 0.01 = m(v'' - v')`
`v'' = -0.03 + 0.06 = 0.03 m//sec`
`v'' = -0.03 + 0.06 = 0.03 m//sec`
`v'' = 3 cm//sec`.