A ball is thrown with a speed of 30 m/s at an angle of 10 degrees. when is the vertical component of the velocity equal to zero? a) when the ball has zero acceleration
b) when the ball first touches the ground
c) at the top of the balls trajectory
d) when the ball is first thrown
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c) at the top of the balls trajectory

Explanation:

If the ball is thrown at an upward angle, the ball will rise upwards to a certain highest point and then change direction and start to fall downwards. All this happens when the ball is also travelling horizontally, which causes the ball to travel in an arc.

If we consider the point where the ball reaches its highest point in its trajectory, we realize that at this point (where the ball actually switches directions from upward to downward), the ball actually momentarily pauses vertically (it still moves horizontally, but it is neither moving up or down)

At this point (i.e at the top of its trajectory), the ball has zero vertical velocity.