A cyclist applies the brakes to slow down. The cyclist and bicycle are treated as one system. The road and air are in the surroundings.

The table accounts for every energy store that changes inside the system during the braking.

Energy store	Change
Kinetic store of the cyclist and bicycle	Decreases by 7600 J
Thermal store of the brake blocks	Increases by 5200 J
Thermal store of the tyres	Increases by 1600 J

Which expression gives the energy transferred across the boundary of the system and its direction?

$J\left[7600-(5200+1600)\right]\ \mathrm{J}$ is transferred from the surroundings to the system

$J\left(5200+1600\right)\ \mathrm{J}$ is transferred from the system to the surroundings

$J\left(5200+1600\right)\ \mathrm{J}$ is transferred from the surroundings to the system

$J\left[7600-(5200+1600)\right]\ \mathrm{J}$ is transferred from the system to the surroundings

A cyclist applies the brakes to slow down. The cyclist and bicycle are treated as one system. The road and air are in the surroundings.

The table accounts for every energy store that changes inside the system during the braking.

Energy store	Change
Kinetic store of the cyclist and bicycle	Decreases by 7600 J
Thermal store of the brake blocks	Increases by 5200 J
Thermal store of the tyres	Increases by 1600 J

Which expression gives the energy transferred across the boundary of the system and its direction?

$J\left[7600-(5200+1600)\right]\ \mathrm{J}$ is transferred from the surroundings to the system

$J\left(5200+1600\right)\ \mathrm{J}$ is transferred from the system to the surroundings

$J\left(5200+1600\right)\ \mathrm{J}$ is transferred from the surroundings to the system

$J\left[7600-(5200+1600)\right]\ \mathrm{J}$ is transferred from the system to the surroundings

8 Energy – forces doing work

8 Energy – forces doing work Questions