22. A 20.0 kg piece of rock starts from rest at the top of the first hill (point

Question

22. A 20.0 kg piece of rock starts from rest at the top of the first hill (point A). It slides down the hill and follows the track as illustrated in the drawing. We will assume that there is no friction for part (a) and (h). (a) Using the conservation of energy concepts, find the kinetic energy of the rock at the bottom of the first hill (point 11). (3 points) (b) What is the rock's speed at point C? (3 points) (c) A second, identical rock slides down the hill, but by now the track has become rough, resulting in a kinetic frictional force exerted on the rock. As a result, the kinetic energy of the rock at point B is only half the value obtained in part (a). Find the work done by the kinetic frictional when the rock reaches point B. (4 points)

Explanation / Answer

a ) 1/2 *m v2 = mgh ------ X

v = 13.28 m/s.

b) enery of block at A = potential enery at C + kinetic energy at c.

mg * 9 - mg*5 = 1/2 m v2.

v= 8.85m/s.

c) at point c

kinetic energy = 1/2 * kinetic energy at A(without).= 1/2 mgh from eq X.

so change in energy = work done by frictional force. = 1/2 * mgh = 882

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