A body of mass 5 kg stJrls from the origin with an initial velocity `bar(u)=(30hati+40hatj)ms^(-1)` .If a constant force `(-6hati-5hatj)N` acts on the body, the time in velocity, which the y-component of the velocity becomes zero is.

Options

A. 5 s
B. 20 s
C. 40 s
D. 80 s

Answer

C

Explanation

From newton's second law of motion,
Force=mass`xx`acceleration
Acceleration along y-axis is
`a_(y)=-(5)/(5)ms^(-2)=-1ms^(-2)`
From equation of motion,
`v_(y)=u_(y)+a_(y)t`
where, `v_(y)` is initial velocity along y-axis, t is the time and `v_(y)` is the final velocity along y-axis.
Given, `v_(y)=0`
`u_(y)=40ms^(-1)`,
`a_(y)=-1ms^(-1)`
`therefore0=40-1xxt`
`impliest=40s`