A 0.21-kg stone is held 1.5 m above the top edge of a water well and then droppe
ID: 1783651 • Letter: A
Question
A 0.21-kg stone is held 1.5 m above the top edge of a water well and then dropped into it. The well has a depth of 4.8 m (a) Taking y0 at the top edge of the well, what is the gravaional potential energy of the stone-Earth system before the stone is released? (b) Taking y = 0 at the top edge of the well, what is the gravitational potential energy of the stone-Earth system when it reaches the bottom of the well? (c) What is the change in gravitational potential energy of the system from release to reaching the bottom of the well? When a 2.70-kg object is hung vertically on a certain light spring described by Hooke's law, the spring stretches 2.88 cm. (a) What is the force constant of the spring? N/m (b) If the 2.70-kg object is removed, how far will the spring stretch if a 1.35-kg block is hung on it? cm (c) How much work must an external agent do to stretch the same spring 9.00 cm from its unstretched position?Explanation / Answer
(A) PE = m g h
PE = 0.21 x 9.8 x 1.5 = 3.09 J
(B) PE = 0.2 1 x 9.8 x - 4.8 = - 9.88 J
(c) change in PE = Pef - Pei = - 12.97 J
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