Chapter 3 Mock Flashcards
Recall equation to calculate the change in gravitational potential energy
Mxgxh
Recall the equation for kinetic energy
0.5 x m x v2
What is meant by conservation of energy
Energy cannot be created or destroyed
State the energy changes in an object projecting upwards or up a slope
Gravitational potential energy
To kinetic energy if it moves
State the energy changes in a moving object hitting an obstacle
Kinetic - elastic + sound +thermal.
State the energy changes in an object accelerating at a constant force
Kinetic energy
State the energy changes in an object slowing down
Kinetic - thermal
State the energy changes in an electric kettle
Electrical- thermal- sound
What happens in energy transfers in a closed system
There is no net change to the total energy In that system
When do mechanical processes become wasteful
When they cause a rise in temperature so dissipating energy In heating the surroundings
Explain ways of reducing unwanted energy give example
E.g.-your home and heat loss- to reduce this you can use: cavity wall insulation, loft insulation and double glazed windows.
How does thermal insulation work
Double glazing windows- trapped air between two panes of glass, air is a poor conductor of heat, reduces heat loss by radiation.
Cavity wall insulation/loft insulation. - putting insulating material such as wool between brick and inside wall, it reduces heat loss by conduction and also stops air circulating inside the cavity therefore reduces heat loss by convection
How thickness and thermal conductivity of the walls of a building on its rate of cooling qualitatively
The thicker the walls the slower the heat takes to escape. Thinner walled buildings will be cooler
Equation for efficiency
Useful energy in / total energy
How to increase efficiency
Reduce amount of wasted energy
