P7.1 Flashcards
What is energy
a quantity in physics measured in Joules
Types of energy stores
Chemical Thermal Kinetic Gravitational Potential Elastic potential Nuclear Electrostatic Magnetic
How is energy transferred
Mechanically using forces.
Electrically using current.
Heating by particles.
Heating by radiation.
Law of conservation of energy
Energy cannot be created or destroyed. Energy can only be transferred between stores.
Suggest why the water is warmer at the bottom of a waterfall
The water at the top has Gravitational Potential Energy
This get transferred to Kinetic Energy
Due to the collision between the water and the rocks Heat is produced
This increases the temperature of the rock
Consequently the water get warmed as well!
What assumption do you make when calculating energy transfer between stores
Zero energy dissipates into the environment as heat –light or sound.
A moving bike with kinetic energy 1.2 X 10 (to the power of 6) J comes to a stop over a distance of 50m. Calculate the force exerted by the brakes.
Follow the energy
Kinetic store transferred to Thermal store mechanically (using forces)
The force exerted by the brakes will do work equal with the initial energy
W = fxd = 1.2x106 J f = 1.2x106 J / d f = 24000 N
A body with mass of 50 Kg is 100m above a spring with k = 500 N/m. The body is released and falls onto the spring.
a. Calculate the EPE that will be stored in the spring.
b. Calculate the spring’s max compression.
c. Calculate the force that the spring exerts on that body at its maximum compression.
A pair of sunglasses has a mass of 25g and is travelling at 2m/s before it hits the sand. Calculate the energy transferred to the thermal store of the surroundings.
We follow the energy :
Kinetic store turns to Thermal Mechanically
Thermal energy = 1/2mv2 = 0.5 x 0.025 Kg x 4 (m/s)2
Thermal energy = 0.5 J
