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

Options

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

Answer

C

Explanation

Here, m=5kg
`bar(u)=(30 hati+40hatj)ms^(-1) and bar(F)=(-6hat i-5hatj)N `
`therefore u_(y)=40ms^(-1) and F_(y)=-5N`
`a_(y)=(F_(y))/(m)=(-5)/(5)=-1ms^(-2), v_(y)=0,`
`"As", v_(y)=u_(y)+a_(y)t or 0=40-1xxt therefore t=40s`