A builder drops a brick of mass 2.5 kg2.5\text{ kg}2.5 kg from a scaffold platform at a height of 5.0 m5.0\text{ m}5.0 m above the ground. Take the acceleration of free fall to be g=9.8 m/s2g = 9.8\text{ m/s}^2g=9.8 m/s2.
(i) Calculate the change in gravitational potential energy of the brick when it is dropped.
(ii) Describe the energy transfers from the moment the brick is released until it is at rest on the ground.
Another builder on the site carries a bucket of mortar up a ladder to the platform. He climbs a vertical height of 4.0 m4.0\text{ m}4.0 m in a time of 8.0 s8.0\text{ s}8.0 s. His total weight, including the bucket, is 600 N600\text{ N}600 N.
(i) Calculate the useful power which his muscles are producing.
(ii) In fact, his body is only 15%15\%15% efficient when climbing the ladder. Calculate the rate at which chemical energy stored in his body is being used.
533 exam-style questions on CIE IGCSE Physics 1.7 Energy, work and power, covering 1.7.1a Energy stores and energy transfers, 1.7.1b Conservation of energy, 1.7.1c Kinetic and gravitational potential energy, 1.7.2 Work done, 1.7.3 Energy resources, 1.7.3a Energy resources and electricity generation, 1.7.3b Nuclear fusion as an energy source, 1.7.3c Efficiency of energy transfer, and 1.7.4 Power. Each one has a worked solution and a mark scheme showing where the marks go.