Moving Reference Frames and Cannon

[fudawala]

This is the question:

A physics lecture demonstration uses a small canon mounted on a cart that moves at constant velocity v across the floor. At what angle theta should the cannon point (measured from the horizontal floor of the cart) if the cannonball is to land back in the mouth of the cannon? Explain clearly your choice of frame of reference.

 

[Fisix]

The horizontal component of the velocity of the cannonball must be equal with the velocity of the cart.

v = vbx = vb.cos θ

cos θ = v/vb

where vb is the velocity of the cannonball

obs. Considering that it happens in the vacuum so there is no drag forces from the fluid (air).