Energy conservation
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Define 'work done' in physics.
Work done is the energy transferred when a force causes displacement. It's calculated as force multiplied by the displacement in the direction of the force: W = Fd cosθ (where θ is the angle between the force and displacement).
State the principle of conservation of energy.
The principle of conservation of energy states that energy cannot be created or destroyed; it can only be transformed from one form to another, or transferred between objects. The total energy in a closed system remains constant.
Define the efficiency of a system.
Efficiency is the ratio of useful energy output to the total energy input, often expressed as a percentage. Efficiency = (Useful energy output / Total energy input) x 100%.
A motor consumes 500J of electrical energy to lift a mass, but only 400J of potential energy is gained by the mass. What is the efficiency of the motor?
Efficiency = (Useful energy output / Total energy input) x 100% = (400J / 500J) x 100% = 80%.
Define power as work done per unit time and give its SI unit.
Power is the rate at which work is done or energy is transferred. It's calculated as P = W / t, where W is work done and t is time. The SI unit of power is the watt (W), equivalent to joules per second (J/s).
How can power be calculated if force and velocity are known?
Power can be calculated as the product of force and velocity: P = Fv, where F is the force applied and v is the velocity of the object in the direction of the force.
A car engine exerts a force of 2000 N to maintain a constant speed of 15 m/s. Calculate the power developed by the engine.
Using P = Fv, the power developed by the engine is P = 2000 N * 15 m/s = 30,000 W or 30 kW.
Describe how energy is conserved in a simple pendulum system, neglecting air resistance.
In a simple pendulum, energy continuously transforms between gravitational potential energy (GPE) at the highest point and kinetic energy (KE) at the lowest point. The total energy (GPE + KE) remains constant throughout the swing.
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