Energy Calculations and Efficiency

The values on the Sankey diagram show that

• 85 J of energy are wasted

• 15 J of energy are useful

• energy is conserved

• the electrical heater is 15% efficient

Fill in the blank

(a)  

Check all of the correct answers

• the light bulb is more efficient

• the heater is more efficient

• the efficiency of the heater is 85%

• the efficiency of the light bulb is 90%

• heat energy is always wasted energy

The energy in a wind turbine is transferred from ______ to _______ (separate your answers with a comma e.g. heat, kinetic)

(a)  

A shopping centre has escalators to move people between floors. A man of mass 78 kg steps on to an escalator.

The escalator lifts him a height of 5.0 m at a speed of 1.2 m/s.

What is his gravitational potential energy at the top of the elevator?

(a)  

A shopping centre has escalators to move people between floors. A man of mass 78 kg steps on to an escalator.

The escalator lifts him a height of 5.0 m at a speed of 1.2 m/s. What is his kinetic energy?

(a)  

A shopping centre has escalators to move people between floors. A man of mass 78 kg steps on to an escalator.

The escalator lifts him a height of 5.0 m at a speed of 1.2 m/s. What is his total energy at the top?

(a)  

The Sankey diagram shows the energy transferred by the panel of solar cells. What is the efficiency of the solar panels?

(a)  

The photograph shows a small airplane, of mass 600 kg.

This airplane has an electric motor powered by fuel cells. Fuel cells use hydrogen gas and provide an electric current.

When the airplane is working, the energy changes are

• chemical → electrical → kinetic

• electrical → chemical → kinetic

• electrical → kinetic → chemical

• kinetic → chemical → electrical

The photograph shows a small airplane, of mass 600 kg.

The velocity of the airplane is 28 m/s.

Calculate the kinetic energy of the airplane.

(a)