Aball is dropped from rest and falls to the floor. the initial gravitational potential energy of the ball-earth-floor system is 10 j. the ball then bounces back up to a height where the gravitational potential energy is 7 j. what was the mechanical energy of the ball-earth-floor system the instant the ball left the floor? (a) 0j (b) 3j (c) 7j (d) 10j

C is the right option

Explanation:

The ball looses energy in the rebound due to ball deformation, heat loss from bounce. Total mechanical energy is not conserved so mechanical energy as it bounces of the floor is equal to transformed potential energy at maximum height of second bounce which is 7j.

- measure reactants precisely. ( first choice)

- stir to the reaction take place. ( second choice)

- wait patiently until the reaction completes. ( fourth choice)

- make sure to recover as much copper as possible. ( last choice)

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i just did this and got a 100.