A 2.00-kg ball has zero potential and kinetic energy.Maria drops the ball into a 10.0-m-deep well.After the ball comes to a stop in the mud,the sum of its potential and kinetic energy is:
A)zero.
B)196 J.
C)-196 J.
D)392 J.

Question

Quizplus · Accepted Answer

When the ball is at the top of the well, it has zero potential and kinetic energy. As it falls, it gains potential energy due to its position in the gravitational field. When it hits the bottom of the well, it stops moving, so it has zero kinetic energy. At this point, its potential energy is equal to the potential energy it had at the top of the well plus the work done by gravity in pulling it down:

PE = mgh = (2.00 kg)(9.81 m/s^2)(10.0 m) = 196 J

Since the ball has zero kinetic energy, the sum of its potential and kinetic energy is:

KE + PE = 0 J + 196 J = 196 J

However, since the question asks for the sum of its potential and kinetic energy after it comes to a stop in the mud, the answer must be negative, since the ball loses potential energy and gains an equal amount of energy in the form of heat due to friction with the mud. Therefore, the best choice is C (-196 J).

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