Extra Explaining Question - WORK, ENERGY AND POWER

WORK, ENERGY AND POWER

1. Describe the energy stored in each of the following
   1. A moving bicycle
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      The energy stored in a moving bicycle is kinetic energy due to its motion.
   2. A compressed spring
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      The energy stored in a compressed spring is elastic potential energy . When spring is compressed, work is done to compress it against its natural state, storing potential energy within the spring
   3. A bowl of breakfast cereal
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      The energy stored in a breakfast cereal is chemical energy stored in the food molecules such as carbohydrates, fats and proteins
   4. A rock lifted off the ground
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      The energy stored in a rock lifted off the ground is gravitational potential energy. As the rock is lifted against the force of gravity, work is done to increase its height, resulting in potential energy.
2. Explain what is wrong with this statement:
   ‘A car battery stores electrical energy for the lights, horn and starter motor’
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   The statement is incorrect because a car battery stores chemical energy, not electrical energy. When the car is running, the alternator converts mechanical energy from engine into electrical energy to recharge the battery and power the lights, horn and starter motor.
3. Describe how the stores of energy change from the beginning to the end of the following processes:
   1. A catapult launches a marble
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      • In the beginning, the potential energy is stored in the catapult’s elastic material.
      • During the launch, the potential energy stored in the catapult’s elastic material is converted into kinetic energy as it moves the marble forward.
   2. A ball rolls along the ground and comes to rest
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      • At the beginning of the process, the kinetic energy is stored as the ball rolls along he ground.
      • As the ball rollsalong the ground, friction force between the ball and the ground converts kinetic energy into thermal (Heat) energy, sound energy until the stop
   3. A butane gas camping cooker heats up a pan of water
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      • At the beginning of the process, the potential energy is stored in the butane gas stored in the camping cooker.
      • When the gas is ignited and burnedchemical energy is converted into thermal (heat) energy which heat up water.
   4. A lump of soft putty falls to the ground
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      • At the beginning of the process, its gravitational potential energy is converted into kinetic energy.
      • As the putty falls to the groundchemical energy is converted into thermal (heat) energy which heat up water.
      • As the putty hits the groundit is converted to thermal (heat) energy and sound energy.
4. Explain why no work is done by a person pushing unmovable wall by a force of 40 N to 72 seconds?
   
5. ‘Energy is lost in the form of friction’ Criticise the truth of this statement from your knowledge of physics and explain the true connection between friction and the loss of energy.
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   “Energy is lost in the form of friction” This statement is wrong because energy is neither be created nor destroyed but can be transformed from one form to another such as heat.
   The correct statement is to say “Due to friction, energy is transformed to another form” such as heat, sound or light.

   • The connection between friction and the loss of energy is such that, friction play a role in converting mechanical energy into other form of energy such as heat, sound or light.