A body starts with some initial velocity along a straight line. After `3 s` it is found to be a distance of `15 m` from the starting point. At `4 s` it is at starting point. What is the initial velocity of the body ? (Assume constant acceleration).

Options

A. `20 ms^-1`
B. `10 ms^-1`
C. `5 ms^-1`
D. `15 ms^-1`

Answer

A

Explanation

`15 = 4 x 3 + (1)/(2) a (3)^2`
`rArr 10 = 24 + 3a`…(i)
`0 = 4 xx 4 + (1)/(2) a(4)^2`
`rArr 0 = 24 + 4a` ….(ii)
From (i) and (ii), `u = 20 m//s`.