Question 517167: A tennis ball is thrown vertically upward with an initial velocity of +6.9 m/s.
What will the ball’s velocity be when it returns to its starting point? The acceleration of gravity is 9.81 m/s squared
Answer by richard1234(7193)   (Show Source):
You can put this solution on YOUR website! Assuming the air resistance is negligible, the ball's returning velocity will be -6.9 m/s. You can use projectile formulas like v = at for constant acceleration, or x = (1/2)at^2 + (v_0)t + (x_0), but the simplest way to do it is to note that the total energy in the ball (potential + kinetic energy) is conserved.
At the starting point, the ball is assumed to have zero potential energy, in which all of its mechanical energy is in the form E = (1/2)mv^2. When the ball reaches the top, its kinetic energy is zero and its potential energy is maximized, and when the ball reaches the ground, its potential energy is zero (or the original potential energy) and its kinetic energy is the same as it originally was (except v is in the opposite direction).
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