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# Physics Chapter 4 work, energy, and power By:Ryan, Grade 11

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• 2.  Work done is when a force moves the point at which it acts in the direction of the force Work done = force*distance moved Work done for displacement x = force*x*cos
• 3.  Work done = pressure*change in volume
• 4.  Ep = mass*gravity*chanhe in height Ek = ½*mass*volume Ep = Ek
• 5.  Efficiency = useful work done/total energy input It may be given as a ratio or percentage
• 6.  It says that if the elastic limit is not exeeded, the extention is proportional to the aplied load Force = constant*extention
• 7.  Strain = ½*constant*extention^2 Strain energy is energy stored in a body due to a change of shape
• 8.  It is the constant for a material of an object Strain = extention/original length Stress = force/area Young modulus = stress/strain
• 9.  The maximum stress a wire could support, if the fracture is gradual it is ductile, if the fracture is sudden it is brittle
• 10.  When the object returns to its original length with a diffrent path because of excess energy
• 11.  How much energy is needed to raise the temperature of a substance Energy needed = mass*spesific heat capacity*temperature change
• 12.  The energy needed to raise the temperature of an object by one degree Energy needed = mass*thermal (heat) capacity*temperature change
• 13.  The energy needed to change the state of an object Energy needed = mass*latent heat of fusion or vaporisation
• 14.  Power = work done/time taken Power = force*speed
• 15.  It is the turning effect of a force, it is defined as the product of the force and the perpendicular distance of the line of action of the force from the pivot Moment of force = force*length*cos
• 16.  A couple consists of 2 forces equal in magnitude, but opposite in direction with diffrent lines of action The tourqe of a couple is the product of one of the forces and the perpendicular distance between the forces
• 17.  It states that for a body to be in rotational equilibrium the sum of the clockwise moments about any point must equal the sum of the anticlockwise moments about the same point
• 18.  The centre of gravity of an object is the point at which the whole weight of the object may be considered to act For a body to be in equilibrium:1. The sum of the forces in any direction must be zero2. The sum of the moments of the forces about any point must be zero