# Work, energy and power – CIE AS Level Physics 9702

Contents:-

• Energy conversion and conservation
1. give examples of energy in different forms, its conversion and conservation, and apply the principle of conservation of energy to simple examples
• Work and efficiency
1. understand the concept of work in terms of the product of a force and displacement in the direction of the force
2. calculate the work done in a number of situations including the work done by a gas that is expanding against a constant external pressure: $$W = \rho \Delta V$$
3. recall and understand that the efficiency of a system is the ratio of useful energy output from the system to the total energy input
4. show an appreciation for the implications of energy losses in practical devices and use the concept of efficiency to solve problems
• Potential energy and kinetic energy
1. derive, from the equations of motion, the formula for kinetic energy $$E_k = \frac{1}{2}mv^2$$
2. recall and apply the formula $$E_k = \frac{1}{2}mv^2$$
3. distinguish between gravitational potential energy and elastic potential energy
4. understand and use the relationship between force and potential energy in a uniform field to solve problems
5. derive, from the defining equation $$W = Fs$$, the formula $$\Delta E_p = mg\Delta h$$ for potential energy changes near the Earth’s surface
6. recall and use the formula $$\Delta E_p = mg\Delta h$$ for potential energy changes near the Earth’s surface
• Power
1. define power as work done per unit time and derive power as the product of force and velocity
2. solve problems using the relationships $$P = \frac{W}{t}$$ and $$P = Fv$$

Video (1:59:33 mins)