Question

A 4 kg projectile has 1400 J of KE when it leaves the ground. If it has 120 J of KE at its highest point how high did it travel???
a 3m
b 30 m
c 32 m
d 35m
e 40m

Answer 1

Usually at the highest point, the k.E = zero.. and yet this problem says its 120J, that means in this problem may the ball hit the ceiling or something :D.. just a detail to think about

any hoo... any idea ? if it has K.E of just 120J, where the rest of the energy go?

Answer 2

rest of the energy is converted into potential energy

Answer 3

Alright. and what is the expression for potential energy?

Answer 4

PE equals mgh

Answer 5

correct.. so now plug in the values .. wil ya? and get h .. !

Answer 6

look mv^2/2 equals mgh so h is v^2/2g

Answer 7

but I do not have velocity

Answer 8

wait wait. hold on.. don't just think of dumb formulae and equate.. what you said earlier.. is right... u said

"rest of the energy is converted into potential energy "
so how much is the potential energy?!

Answer 9

oh yeah I got it))

Answer 10

so can you tell me how much answer you get noW?

Answer 11

32 m

Answer 12

correct ;-)! congrats!

Answer 13

Could you tell me then in what cases Tension force is constant in dynamics???