Question

a body is projected such htat its kinetic energy at the top is 3/4 th of its initial kinetic energy . what is the initial angle of projection with the vertical ? a] 60

b] 30] c]37

d] 45

. explain the solution

Answer 1

As there is no acceleration in the horizontal direction the velocity component will remain same as vcos∅  and at highest vertical component will be zero. so total velocity at top will be vcos∅

K.E will be 1/2 m (vcos∅)² 

initial energy will be 1/2 mv²

at the highest point 

K.E = 3/4 of initial K.E

1/2 m(vcos∅)² = 1/2 mv²× 3/4

∅= 30°

Correct choice is (B)