P1 Conservation and dissipation of energy

What is the law of conservation?

Energy can be transferred, stored or dissipated but not created or destroyed

What is Work done?

Work done is defined as the amount of force needed to move an object a certain distance

Equation for Work done?

Work done (J)= Force (N) x Distance (m)
W=f x s

Equation for Gravitational Potential energy store?

G.p.e (J)= mass (kg) x gravitational field strength (n/kg) x height (m)
Ep= m x g x h

Equation for kinetic energy store of moving object?

kinetic energy store ( J) = 1/2 x mass(kg) x (speed)² (m/s)
Ek= 1/2 x m x v²

The equation for Elastic potential energy stored in stretch spring?

Elastic potential energy (J)= 1/2 x spring constant (N/m) x (extension)² (m)
Ee= 0.5 x k x e²

Efficiency Equation?

Useful output ÷ total energy input

Way to increase efficiency of an intended energy transfer?

Lubrication
use of thermal insulation
make objects streamlined to reduce air resistance

Define power?

Power is the rate at which energy is transferred or the rate at which work is done.

Equation for power?

Power ( watts)= energy transferred/time
Power = work done/time

What is 1 joule per second equivalent too?

1 joule per second = 1 watt

One joule is equal too?

1 newton metre

A marble is lifted up and placed at the top of a ramp. It then rolls down the ramp and across the floor. It eventually comes to rest. At which point in its journey is its kinetic energy the greatest?

At the bottom of the ramp when it has just got to ground level

At this point all of the gravitational potential energy has been transferred to kinetic energy and the marble will be at the highest speed in the journey.

What is the main energy transfer for a long-distance runner?

Chemical energy into kinetic energy

Which one of these statements is the best explanation of the relationship between the terms 'heat' and 'temperature'?

Heat and temperature are not the same because sometimes supplying heat to something causes a change in state instead of a change of temperature

Where is energy dissipated?

Energy is dissipated into its surroundings

What is a way to reduce unwanted energy transfers?

Lubrication or the use of thermal insulation

A buggy with a child in it is being pushed up a ramp to reach a bridge. The loaded buggy weighs 200 N and the bridge is 10 m above ground level. If it takes 30 s to push the buggy up there, what is the power output of the person pushing?

work done = force x distance
power =work done divide time
2000 divide 30
=66.7W

How many hours could 1 x 106 joules of energy keep a 60 W bulb lit for? Give your answer to the nearest hour

5 hrs

Equation for percentage efficiency?

useful enerfy divide total input x100

In an electric kettle, what energy is not wasted and what energy is wasted?

energy that heats the water and infrared radiation dissipates to surrounding from internal energy heating the kettle

What may cause a pendulum to slow down?

Friction( resisting force)

What is a closed system?

a system where no energy can leave