The Table shows the energy transfers in a car engine each second.

Table

Energy transfer	Energy in $kJ\text{kJ}$
energy supplied from the chemical store of the fuel	200
energy transferred usefully to the kinetic store of the car	50
energy transferred to the thermal store of the engine and exhaust gases	120
energy transferred by sound	4
energy transferred by heating due to friction between moving parts	$X$

Calculate the value of $X$ .

Calculate the efficiency of the engine.

The moving parts of the engine rub against each other.

Explain why this mechanical process is described as wasteful.

Suggest how the engine designer could reduce the value of $X$ .

The Table shows the energy transfers in a car engine each second.

Table

Energy transfer	Energy in $kJ\text{kJ}$
energy supplied from the chemical store of the fuel	200
energy transferred usefully to the kinetic store of the car	50
energy transferred to the thermal store of the engine and exhaust gases	120
energy transferred by sound	4
energy transferred by heating due to friction between moving parts	$X$

Calculate the value of $X$ .

Calculate the efficiency of the engine.

The moving parts of the engine rub against each other.

Explain why this mechanical process is described as wasteful.

Suggest how the engine designer could reduce the value of $X$ .

3.2 Dissipation and efficiency

3.2 Dissipation and efficiency Questions