# physics

Lance threw a ball straight up into the air. The ball's gravitational potential energy at its peak height was 0.4 joules, and its speed when it hit the ground was 4 meters per second. What was the mass of the ball?

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1. (1/2) M V^2 = 0.4 J

You know V. Solve for M.

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2. If the equation you're using is (1/2)M*V^2= J and you know J is o.4 just fill in the velocity(speed) and work it out. Here's how I worked it:

(1/2)M*4^2 = 0.4 (change the numbers around)
(Now it looks like:)

0.4/4^2/(1/2) = M (divide 0.4 by 4^2)

0.4/4^2 = 0.025 (then the answer by 1/2)

0.025/(1/2) = 0.050 or 0.05

so your answer is that the mass of the ball Lance threw is 0.05-kg.

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