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Work and Energy Cheat Sheet (DRAFT) by

for students of grade 9

This is a draft cheat sheet. It is a work in progress and is not finished yet.

WORK

POSITIVE
NEGATIVE
ZERO
force acts in the direction of motion of the body
force acts opposite to the direction of motion of the body
force acts perpen­dicular to the direction of motion of the body
ex. work done by gravit­ational force on a freely falling object
ex. work done by gravit­­at­ional force on a lifting object
ex. work done by sun on the planets moving around it
work is the product of force and displa­cement, SI unit: Joules.
1 Joule is the amount of work done on an object when a force of 1N displaces it by 1m along the line of action of the force.
work: scalar; work done: vector.
for work to be done, a force should act on the object and it must be displaced.
1kJ = 1000J

ENERGY

POTENTIAL ENERGY
KINETIC ENERGY
energy present in an object by virtue of its positi­on/­con­fig­uration
energy possessed by a moving body by virtue of its motion
an object having the capability to do work is said to possess energy. SI unit: J
1J is the energy required to do 1J of work.
gravit­ational P
E
 of an object at a point above ground is the work done in raising it from the ground to that point against gravity. P
E
of an object at a height depends on the ground level. depends on the difference in vertical heights of the initial and final positions of the object and not on the path along which the object is moved.
  

LAW OF CONSER­VATION OF ENERGY

energy can only be converted from one form to another; it can neither be created nor destroyed. the total energy before and after transf­orm­ation remains the same.
P
E
+K
E
of an object = its total mechanical energy

POWER

rate of doing work/rate of transfer of energy. SI unit: Watt [James Watt]
1 watt is the power of an agent, which does work at the rate of 1J/s; power is 1W when rate of consum­ption of energy is 1J/s.
1W = 1J/s
1kW = 1000W or 1000J/s