A mine lift raises a cage containing equipment through a vertical height of 45 m. The total mass of the cage and equipment is 12 000 kg12\,000\ \mathrm{kg}12000 kg and the journey takes 30 s.
Gravitational field strength is 10 N/kg.
Calculate the mean useful power output of the lift.
On a second journey, the total mass of the cage and equipment is 15 000 kg15\,000\ \mathrm{kg}15000 kg. The lift raises the cage through the same vertical height with the same mean useful power output.
Calculate the time taken for the second journey.