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In a projectile motion, power of the gra...

In a projectile motion, power of the gravitational force

A

is constant throughout

B

in negative for first half, zero at topmost point and positive for rest half

C

varies linearly with time

D

is positive for complete path

Text Solution

Verified by Experts

The correct Answer is:
B, C
Power = `vecF . vecV` , angle between `vecF and vecV` changes through out the motion as `vecF` is acting vertically downwards so power is not constant.
For first half angle is obtuse, at highest point is perpendicular to and for `2^(nd)` half the angle is acute
`implies` P is negative for first half, zero at topmost point and positive for rest half `implies` (B) is correct.
`P = vecF . vecV = mg hatj cdot [ u cos theta hati + (u_y - gt) hatj] = mgu_(y) - mg^2 t implies ` P change linearly with t.
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