University:
Dakota State University
Course:
PHYS 111 | Introduction to Physics I
Academic year:

2019
Views:

224

Pages:

2
Author:

imophulebf5

Conservation of Energy Worksheet Name: State the law of conservation of energy. Energy is neither created nor destroyed. It can be transferred. A 200-kg boulder is 1000-m above the ground. a) What is its potential energy when it is 1000-m above the ground? PE = mgh = 200 * 9.8 * 1000 = 1,960,000 J b) What is its kinetic energy when it is 1000-m above the ground? KE = 1/2 * m * v² = 0 J c) The boulder begins to fall. What is its potential energy when it is 500-m above the ground? Where did the "lost" potential energy go? PE = mgh = 200 * 9.8 * 500 = 980,000 J It was converted to kinetic energy. d) What is the kinetic energy of the boulder when it has fallen 500-m? PE + KE = 1,960,000 J 980,000 J + KE = 1,960,000 J KE = 980,000 J e) What is the kinetic energy of the boulder just before it hits the ground? 1,960,000 J, because there is no potential energy. A rollercoaster is designed as shown below. If the rollercoaster starts at the top of the first hill from rest, describe what will happen to the rollercoaster. How could you fix this problem? rollercoaster track It would not make it to the top of the 2nd hill. The 1st hill should be taller than the 2nd hill. 4) When you use a slingshot to fire a rock you stretch the rubber band storing potential energy. If you stretched the rubber band so that it had 100-J of potential energy, a) With how much kinetic energy will the rock leave the slingshot? 100 J b) With how much kinetic energy will the rock leave the slingshot if it loses 10-J to heat & sound? 100 - 10 = 90 J 5) A pendulum has 15-J of potential energy at the top of its swing. a) What is its kinetic energy at the bottom of its swing? 15 - 3 = 12 J b) At another time the pendulum has 8-J of potential energy. What is its kinetic energy? 15 - 8 = 7 J c) For the pendulum in "b", what will its kinetic energy be if it loses 2-J to heat? 15 - 2 = 13 - 8 = 5 J 6) A 1-kg ball is 10-m above a table when it is dropped. It bounces to a height of 7-m. a) How much energy is transferred to heat & sound during the bounce? 1 x 10 x 9.8 = 98 J 1 x 7 x 9.8 = 68.6 J 98 - 68.6 = 29.4 J b) Explain why this ball cannot bounce to a height of 12-m if it is dropped. Because you cannot gain energy. It started at a height of 10 m and can't gain energy. c) What could you do to make the ball bounce to a height of 12-m? Have a force applied to the ball OR start the ball at a higher height than 12 m.

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