Question

A body is projected at an angle of 30 to the horizontal with kinetic energy 50 years old the kinetic energy of

Answer 1

Answer:

The information given in the problem tells us that the initial kinetic energy is:

KE=40J=12mV2

∴mV2=80

The body loses all its vertical velocity when it reaches the highest point, but the horizontal velocity remains unchanged at Vx=Vcos30. So the kinetic nergy at the highest point is:

KE=12m(Vcos30)2

or

KE=12mV2(cos30)2

but mV2=80 (from above)

KE=12(80)(cos30)2=30

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But the quickest way to solve this problem is to recognize that, at the highest point, the body loses all of its vertical kinetic energy. So it loses kinetic energy due to its vertical component of velocity =Vsin30

Ratio of energy lost = KEverticalKEtotal=12m(Vsin30)212mV2=(sin30)2=0.25