Work & energy worksheet with answers

A hoist lifts a 400 kg load at constant speed through a height of 26 m in 45 s. Find the average power P it delivers to the load, in kW.

A small ball hangs on a light string of length 1.5 m. It is pulled aside until the string makes 45° with the vertical and released from rest. Ignoring air resistance, find its speed v at the lowest point.

A block slides from rest down a slope at 35° to the horizontal. The coefficient of kinetic friction is 0.15. Find its speed v after it has slid 14 m along the slope.

A toy launcher has a vertical spring of stiffness 400 N/m. A 0.25 kg ball is placed on it and the spring is compressed by 8 cm, then released. Ignoring air resistance and the spring’s mass, find the height h the ball rises, measured from its position when the spring was compressed.

A 4 kg block rests on a rough horizontal table (μ = 0.15). A light string runs from it over a smooth pulley at the edge of the table to a hanging 6 kg block. The system is released from rest. Find the speed v of the blocks after the hanging block has dropped 3 m.

A spring of stiffness 2000 N/m at the bottom of a 25° slope is compressed by 15 cm against a 0.5 kg block and released. The coefficient of kinetic friction between block and slope is 0.1. How far d up the slope does the block travel from the release point before it stops? (Ignore the short distance over which the spring pushes, i.e. take friction and gravity over the whole distance d.)