A circus performer is shot out of a cannon and flies over a net that is placed horizontally 5.3 m from the cannon. When the cannon is aimed at an angle of 30° above the horizontal, the performer is moving in the horizontal direction and just barely clears the net as he passes over it.

How high is the net?

I'm not sure if the height of the net is equal the maximum height of the trajectory.. is it?

Question

A circus performer is shot out of a cannon and flies over a net that is placed horizontally 5.3 m from the cannon. When the cannon is aimed at an angle of 30° above the horizontal, the performer is moving in the horizontal direction and just barely clears the net as he passes over it.

How high is the net? 

I'm not sure if the height of the net is equal the maximum height of the trajectory.. is it?

anonymous · Answer

yes, your assumption is correct :)

carmuz · Answer

Maybe it is, maybe is not. Assume that is not. ;-)|dw:1392422210088:dw|

anonymous · Answer

If I assume that it is not, then how will i determine the height of the net?

anonymous · Answer

It is the correct assumption. If the only component of movement (velocity) is horizontal, there is no vertical component, so by definition of parabolic flight that is the highest point.

anonymous · Answer

I'm sorry but I did not get your explanation..
correct me if i'm wrong, but it follows a parabolic path, which means that there are vertical and horizontal components, so it means that it is not the highest point? O.o
sorry i'm confused right now..

carmuz · Answer

Hummmmm....I think you both are right: "the performer is moving in the horizontal direction and just barely clears the net as he passes over it." means hightest point. Yes. Sorry.

anonymous · Answer

in a parabolic flight, you can consider the x and y parts independently. horizontal velocity is constant throughout with no air resistance. The vertical velocity has an initial value (vsin30), but there is an acceleration due to gravity of -9.8m/s2. The highest point (before it starts to fall) will be when the acceleration has caused the vertical velocity to decrease to 0. It will then begin to accelerate back down. So no vertical velocity implies the highest point it will reach.

anonymous · Answer

aahh..okay? so why will the height of the net be the highest point?

carmuz · Answer

I'm sorry for confusing you, @Data_LG2. Didn't get the "the performer is moving in the horizontal direction" phrase. @furnessj is right. There's no vertical velocity, therefore, highest point is reached.

anonymous · Answer

because the question implies that at the net, the vertical component of velocity is zero, so that is also the highest point. even knowing that, the solution is non-trivial..

anonymous · Answer

*facepalm*
oh yeah! smh

i got it before, but then i got confused  and now i get it again ^.^
i missed "the performer is moving in the horizontal direction"... thanks again @carmuz

Thanks for the explanation @furnessj  (^_^)

are you both physics teachers? O.O i just read your profiles

anonymous · Answer

I have taught physics, yes. I am currently a private tutor. I want to see you solve this now..!