Work, energy and power

Learning objectives

Calculate the work done by a constant force from W = Fs cosθ, and obtain the work done by a varying force from the area under a force–displacement graph, including the elastic potential energy ½kx² stored in a stretched spring

Apply the expressions for kinetic energy Ek = ½mv² = p²/2m and for the change in gravitational potential energy close to the Earth's surface, ΔEp = mgΔh

Apply the principle of conservation of energy to mechanical systems, accounting for energy transferred to the internal energy of the surroundings by friction and drag

Calculate power from P = W/t and from P = Fv, and determine efficiency as the ratio of useful output energy or power to total input

Solve problems using energy methods where the equations of motion would be impractical, such as finding the speed of a body at the foot of a curved frictionless track

Analyse the energy transfers in elastic and inelastic collisions, and account for the kinetic energy that is not conserved