Review work and energy
Physics
•What is the law of conservation of energy?
•What does it mean for this unit?
•Energy is conserved – cannot be created nordestroyed – but can change forms
•Total initial energy = total final energy
•True or false about work?
•A. Work is a form of energy.
•B. A Watt is the standard metric unit of work.
•C. Work is a time-based quantity; it isdependent upon how fast a force displaces anobject.
•D. The force of friction acts upon a softballplayer as she makes a headfirst dive into thirdbase. This is an example of work being done
•Red = true
•A. Work is a form of energy.
•B. A Watt is the standard metric unit of work.
•C. Work is a time-based quantity; it isdependent upon how fast a force displaces anobject.
•D. The force of friction acts upon a softballplayer as she makes a headfirst dive into thirdbase. This is an example of work being done
•True or False on Power
•A. Power is a time-based quantity.
•B. Powerful people or powerful machines aresimply people or machines which always do alot of work.
•C. If person A and person B do the same jobbut person B does it faster, then person Adoes more work but person B has morepower
•Red = true
•A. Power is a time-based quantity.
•B. Powerful people or powerful machines aresimply people or machines which always do alot of work.
•C. If person A and person B do the same jobbut person B does it faster, then person Adoes more work but person B has morepower
•True or False for Kinetic energy
•A. Kinetic energy is the form of mechanicalenergy which depends upon the position ofan object.
•B. If an object is at rest, then it does not haveany kinetic energy.
•C. If an object is on the ground, then it doesnot have any kinetic energy.
•Red = true
•A. Kinetic energy is the form of mechanicalenergy which depends upon the position ofan object.
•B. If an object is at rest, then it does not haveany kinetic energy.
•C. If an object is on the ground, then it doesnot have any kinetic energy.
•True or False – potential energy
•A. Moving objects cannot have potentialenergy.
•B. Potential energy is the energy stored in anobject due to its position.
•C. Both gravitational and elastic potentialenergy are dependent upon the mass of anobject.
•D. If the mass of an elevated object is doubled,then its gravitational potential energy will bedoubled as well.
•True are red
•A. Moving objects cannot have potentialenergy.
•B. Potential energy is the energy stored in anobject due to its position.
•C. Both gravitational and elastic potentialenergy are dependent upon the mass of anobject.
•D. If the mass of an elevated object is doubled,then its gravitational potential energy will bedoubled as well.
•D all have same speed
•RECALL: PE = KE so same height – so PE at topis max and KE is max at bottom – same totalenergy – so since same object the KE = 1/2mv2so same object has same speed at bottom
•Due to conservation of energy!
•Works going up too – if same distance andsame object
•72kg Barry Uhm is at rest on top of a 30mhill, he then slides down the hill and goes upanother hill that is 10m high. How fast is hegoing on top of the 10m high hill? Showenergy bar chart.
• PE + KE PE + KE
•mgh + 0 = mgh + 1/2mv2
•(72kg) (9.8m/s2) (30m) = (72kg) (9.8m/s2)10m) + ½ (72kg) v2
•V = 19.7m/s