Answer to Question #221963 in Physics for caleb villarreal

Question

1. A pendulum has 19J of potential energy at the top of its swing. 
2. What is its kinetic energy at the bottom of its swing? 
3. At another time the pendulum has 7J of potential energy. What is its kinetic energy? 
4. For the pendulum in “b”, what will its kinetic energy be if it loses 2J to heat? 

Answer 1

(a) By the law of conservation of energy, we have:

$$KE_{top}+PE_{top}=KE_{bottom}+PE_{bottom},$$ $$0+PE_{top}=KE_{bottom}+0,$$ $$KE_{bottom}=PE_{top}=19\ J.$$

(b) If the pendulum has 7 J of potential energy, than the rest of the energy of the pendulum is kinetic energy. Therefore, the pendulum has 12 J of kinetic energy.

(c) If the pendulum loses 2 J to heat its kinetic energy be 10 J.