Work

WORK

By Mr Math n Physics

• Mechanical work is done when an object is moved over a distance by a force applied in the direction of its displacement

• It is said that the force does work on the object

• If a force is applied to an object but doesn’t result in any movement, no work is done

​Work Done

• When work is done, energy is transferred

• Work done and energy transferred are equivalent quantities

Work Done

Formula Work Done

​W = work done, measured in newton-metres (N m)
F = force applied, measured in newtons (N)
d = distance in metres (m)
∆E = energy transferred, measured in joules (J)

A car moving at speed begins to apply the brakes. The brakes of the car apply a force of 500 N, which brings it to a stop after 23 m. Calculate the work done by the brakes in stopping the car.

Worked Example

Multiple Choice

A trolley is pushed with a force that causes it to move a certain distance. It moves in the direction it is pushed. Which row in the table represents the combination of force and distance that means the smallest amount of work is done on the trolley?

• A

• B

• C

• D

Multiple Choice

A force acts on an object and causes the object to move a certain distance, in the same direction as the force. Which row represents a situation in which the largest amount of work is done on the object by the force?

• B
• C
• A
• D

Multiple Choice

A box of weight of 1500 N raised vertically by 3.0 m

calculate the work done on the box

• 6000 J
• 1500 J
• 4500 J
• 3000 J

Multiple Choice

The mass of metal block is 0.2 kg. The vertical height of B above A is 0.6 m. The acceleration due to gravity is 10 m/s²

Calculate the work done in lifting the block from A to B

• 0.6 J
• 1.2 J
• 0.8 J
• 2.0 J

Multiple Choice

A 1000 kg of car move at speed 72 km/h. it is slowed down by break system until it stop. what is work done by the break system of the car ? 

• 150000 J
• 250000 J
• 100000 J
• 200000 J

Multiple Choice

Work done by a force on a resting object is 100J. Find the new speed of the object if the mass of the object is 2 kg.

• 10 m/s
• 20 m/s
• 15 m/s
• 5 m/s

Multiple Choice

A box of mass 2.0 kg and weight 20 N is carried to the top of some stairs. What is the work done against gravity on the box ?

• 10 J
• 24 J
• 30 J
• 15 J

Multiple Choice

A box is initially at rest at the top of a rough slope. The box slides down the slope. The weight of the box is 20 N. The slope is 4.0 m long and 2.0 m high. The box does 10 J of work against friction as it slides down the slope. What is the speed of the box as it reaches the bottom of the slope?

• 7.20 m/s
• 5.43 m/s
• 3.00 m/s
• 4.50 m/s

Multiple Choice

A stationary box of mass 2 kg is placed at a height of 5 m on a slope. Upon release, it begins to slide 10 m down the slope, as shown in the following diagram. Take g = 10 N kg⁻¹.

 Determine the energy lost due to friction if the slope is not frictionless and the velocity of the box at the bottom of the slope is 6.0 m s^–1.

 

• 64 J
• 48 J
• 32 J
• 80 J

Multiple Choice

In the Swissôtel Vertical Marathon 2010 that took place at Raffles City, each competitor had to climb 1336 steps to reach the top of the building. If each step is approximately 20 cm high, determine the minimum work done required by a vertical marathon runner, who weighs 600 N, to reach the top of the building. Take g = 10 N kg⁻¹.

• 1.2 x 10⁵ J

• 2.0 x 10⁵ J

• 1.5 x 10⁵ J

• 1.6 x 10⁵ J