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Work done

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Work for KS4

1. Calculation of work performed

1.1. Work of a force acting in the direction of motion of a body

1.2. Work of a force acting in the opposite direction to the motion of a body

1.3. Work of a force acting at an angle to the direction of motion of a body

2. Work and energy

3. Forum

↓ Show theory [1] ↓

Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:work_done/5049/

Example 1.

Which of the following statements about work is true?

The work done by a body is greater when more time is expended.
The force acting in the opposite direction to the movement of a body does not do any work.
When an electric drill is used to make a hole in a wall, work is done by the electric drill.
A groom lifts his bride from the ground to a height and then walks a distance ahead. He only does work when he is lifting the bride.
A force is used to stop the downward movement of a trolley. Work is done on the trolley.
We applied a push to a cabinet, but it does not move. Our work is zero.
A car that moves faster does more work than a car that moves slower on the same route, considering air resistance.
Satellite orbits the Earth above the equator at an altitude of 36,000 km. During orbit, the attractive force (centripetal force) between the Earth and the satellite does the work.
Current water from a dam falls on a power plant's turbines. In doing so, it does the work.

Example 2.

Dad pulls a sled up a 45 m long slope. If he pulls it with a power of 30 W, he will pull the sled to the top in half a minute.

How much work does dad do?
With how much force does dad pull the sled to the top?

A trolley on a smooth horizontal surface is pushed with a force of 20 N. Calculate the work done if the trolley covers a distance of 100 m.

Tom slides down a slope into a horizontal plane. If the plane has a frictional force of 48 N and Tom covers a distance of 20 m on the plane before stopping, how much work is done to stop Tom on the plane, and what does the work?

A log is acted upon by a force of 40 N at an angle of , as shown in the figure. If the log moves a distance of 4 m due to the force. How much work is done?

An elevator, having a mass of 800 kg, is uniformly lifted to a height of 18 m. How much work is done by the elevator motor?

A car with a mass of 1400 kg accelerates at . How much work is done by the car engine after moving a distance of 100 m?

The locomotive of a train pulls it with a force of 8 kN. If the train is moving evenly at a speed of . How much work does the locomotive do in one hour?

When a force F is exerted on a log and moved a distance s, a work W is done. How much work will be done when half of the force is exerted and the log is moved twice the distance?

10.

Three identical crates, each weighing 60 kg and 40 cm high, lie on the ground. We need to stack them on top of each other. How much work will we do?

11.

2000 litres of water fall from a height of 16 m. How much work is done by the water?

The specific gravity of the water is .

12.

A flowing water acts with a force of 100 N perpendicular to the blades of the mill wheel with a radius of 2 m. How much work does the water do when the wheel turns 10 times?

13.

Three forces act on the wooden log, as shown in the figure below. The applied force is 14 N, the frictional force is 10 N and the vertical force is 16 N. Calculate the work of each force and the total work done by the forces in moving the log through a distance of 6 m.

14.

Dave pushes a trolley with a force of 12 N at a distance of 20 m.

How much work did he do?
How far does the trolley have to move with the same force in order to do 1 kJ of work?

15.

Express the unit of work (J) in base units of measurement (m, kg, s).

16.

A 6 kg body is acted upon by a force of 3 N for 10 s. How much work is done if the initial velocity of the body is zero?

17.

An airplane weighs 600 kg. The engine of the airplane works with a power of 70 kW and performs 8.4 MJ of work for 6 km of uniform horizontal flight.

How long does the plane fly 6 km on such a flight?
What is the thrust force of the engine on the plane?
Calculate the speed of the plane.
What is the kinetic energy of the plane?
What is the force of the air resistance against the airplane during the flight?

18.

A force of acts on an object. The work done by the force is . How far does the object move in the direction of the force?

19.

A boy uses a rope to pull an object of mass up a slope. The rope is parallel to the slope. The tension in the rope is constant and of value . The object moves a distance along the slope and rises through a height . How much work is done by the boy?

20.

Two men, X and Y, try to move identical heavy boxes, P and Q. Man X tries to push box P along the floor. The box does not move because an object is in the way. Man Y lifts box Q from the floor onto a shelf.

Which man does the most work on their box, and which box gains the most energy?

	man doing most work	box gaining most energy
A	X	P
B	X	Q
C	Y	P
D	Y	Q

21.

A moving object is brought to rest by a resistive force of over a distance of . What is the work done by the force?

22.

In some situations, a force does work. Which set of conditions increases the quantity of work done by the force?

	magnitude of force	distance moved by the force
A	decreases	decreases
B	decreases	stays the same
C	increases	increases
D	stays the same	decreases

23.

A toy car is pushed a distance of with a force equal to . How much energy is transferred?

24.

A weight is raised through a height of . How much work is done by the force?

25.

What is the unit of work?

26.

A skier is pulled up a short straight slope at constant speed by a rope.

The tension in the rope is and there is a combined frictional and air resistance force of acting on the skier. The slope is long and the skier rises vertically. How much work is done by the rope pulling the skier up the slope?

27.

A force acts on an object and the object moves a distance in the direction of the force. What is the work done on the object?

28.

A force does work moving an object in the direction of the force. Which change in the force and distance always increases the work done?

	force	distance
A	greater	same
B	greater	smaller
C	same	smaller
D	smaller	smaller

29.

A car has of kinetic energy. The car brakes and stops in a distance of . What is the average braking force acting on the car?

30.

Which situation involves no work being done and no energy being transferred?

a car skidding to a stop on a road
a crane lifting a load
a heavy load hanging from a strong bar
a student dragging a big box over a rough floor

31.

A builder lifts 30 bricks from the ground onto a platform high. Each brick has a mass of . What is the work done against gravity by the builder in lifting the bricks onto the platform?