Question

Question #703f0

Answer 1

The horizontal component has no effect on the vertical component of the balls' motion (there is also no component of gravity that acts in the horizontal direction)

Explanation:

The question assumes no air resistance. In this case, there is only one force acting on the balls, that is the force due to gravity. This acts in the vertical direction only.

You need to consider the vertical and horizontal components of the balls' motion separately. Since they are at 90 degrees to each other, the horizontal and vertical components do not affect each other.

For the first ball:
There is no horizontal component. The ball accelerates towards the earth at a rate of `g=9.81ms^-2` due to gravity (per Newton's 2nd law: `F=ma` . In this case `"Force" =weight` therefore `ma=mg`therefore `a=g`)

For the second ball:
Horizontal component: There is no force acting in the horizontal direction. Newton's 1st law tells us it will carry on moving with the same velocity in the horizontal direction unless acted upon by a force. Hence the horizontal velocity does not change during the flight of the second ball (i.e. its change in horizontal velocity is nil in the absence of air resistance)

Vertical direction: The acceleration in the vertical direction is due to the force of gravity. This is the same as for the first ball.

Hence both balls start with zero initial velocity in the vertical direction. They both accelerate at the same rate (`g`) hence they both change velocity at the same rate in the vertical direction.

Hence the answer is C