Topic 1.3: Work, Energy and Power Questions

A box is dragged at a steady speed across a rough floor by a horizontal rope.

Identify the unit of work done, and explain why the weight of the box does no work as it is dragged.

A 1.5 kg watering can is lifted from the ground onto a shelf 1.2 m high.

Taking g = 9.8 N kg⁻¹, calculate the gravitational potential energy it gains.

A 0.40 kg hockey ball is struck and moves at 30 m s⁻¹.

Calculate its kinetic energy.

State what the area under a force–extension graph for a spring represents.

A coin falls from rest off the edge of a table.

Air resistance is negligible.

State the quantity that stays constant as the coin falls.

State what is meant by the work done by a force.

State the principle of conservation of energy, and identify the form into which most of the energy wasted by a real machine is transferred.

State the SI unit of power and express it in terms of the joule and the second.

Sketch a force–distance graph for a constant 10 N force acting over a distance of 4.0 m, and indicate on your sketch how the work done is found from the graph.

State what is meant by the kinetic energy of an object.

A 1.5 kg melon is dropped from rest off a balcony 8.0 m above the ground.

Air resistance is negligible and g = 9.8 N kg⁻¹.

Calculate the gravitational PE it has at the top, and use conservation of energy to find its speed just before it hits the ground.

A spring obeys Hooke's law.

A force of 18 N stretches it by 3.0 cm.

(a) Determine the spring constant.

(b) Determine the elastic potential energy stored in the spring at this extension.

A spring of spring constant 500 N m⁻¹ is compressed by 4.0 cm and then released, transferring all of its stored energy in 0.025 s.

(a) Calculate the elastic potential energy stored in the spring.

(b) Calculate the average power delivered as the spring releases this energy.

A spring gun stores 4.5 J of elastic potential energy when its spring (spring constant 900 N m⁻¹) is fully compressed.

Calculate the compression of the spring, in centimetres.

A worker pushes a trolley 8.0 m along a corridor using a handle inclined at 60° to the horizontal floor.

The push along the handle has magnitude 15 N.

Calculate the work done by this push on the trolley.

During a test, a spring stores 200 J of elastic potential energy when it is compressed by 50 cm.

Estimate the spring constant of the spring.

A pendulum bob of mass 0.25 kg is pulled to one side so that it is raised 0.20 m above its lowest point, then released from rest.

Air resistance and friction are negligible and g = 9.8 N kg⁻¹.

Determine the speed of the bob as it passes through the lowest point of its swing.

The force on a model rocket sled varies with distance and is plotted on a force–distance graph as a curve that bulges above a straight line.

The grid is marked so that each small square represents 2.0 N by 0.50 m.

By counting squares, a student estimates the region under the curve from 0 to 4.0 m contains about 45 small squares.

Estimate the work done on the sled over this distance.

A constant net force of 16 N acts on a 2.5 kg cart, initially at rest, over a distance of 5.0 m.

Show that the final speed of the cart is approximately 8 m s⁻¹.

A 0.040 kg golf ball rolls off a shelf and falls from rest through a height of 2.5 m.

Air resistance is negligible and g = 9.8 N kg⁻¹.

Determine the speed of the ball just before it lands.