Lesson objectives

3.1.1 demonstrate the concept of work using equation W= force × distance in the direction of the force

3.1.2 Solve problem using the equation  W=F× d

 

Work is the product of force and the distance moved by the force in the direction of force.

In Physics, work is done when an object is moved over a distance by an external force applied in the direction of its displacement.

When a force of one newton moves its point of application by one metre in the direction of force, one joule of work is done

 

Work is done when a force is used to move an object over a distance.

• When work is done, energy is transferred from one object to another
• Work done can be thought of as the amount of energy transferred, hence its units are in Joules (J)
• Usually, if a force acts in the direction that an object is moving then the object will gain energy
• If the force acts in the opposite direction to the movement then the object will lose energy

Revision Questions

 

1.    What needs to be known to calculate the work done by a force acting on an object?

 

 

2.    In a factory, 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 the box, and which box gains the most energy?

3.    A person in a factory has to lift a box on to a shelf.

 

Which action involves the person doing the least amount of work?

A lifting the box quickly to the high shelf

B lifting the box slowly to the high shelf

C lifting the box to the low shelf first then lifting it to the high shelf

D lifting the box to the low shelf instead of to the high shelf

 

4.    In the following list, tick the two boxes next to the two quantities needed to calculate the work done on an object

 

5.    Three boxes each weigh 100N. A man lifts all the boxes together from the ground on to a shelf that is 1.5m above the ground.

. What work is done by the man?

 

6.    A force F moves a load from the bottom of a slope to the top

 

The work done by the force depends on the size of the force, and on a distance. What is this distance?

 

7.    The diagram shows a barrel of weight 2.5 × 10³ N on a frictionless slope inclined at 40° to the horizontal.

A force is applied to the barrel to move it up the slope at constant speed. The force is parallel to the slope. What is the work done in moving the barrel a distance of 6.0 m up the slope?

 

8.    A box weighs 45 N. Calculate the work done in lifting the box through a vertical height of a 4 m   b   67 cm

9.    A force of 36 N acts at an angle 55 to the vertical. The force moves its point of application by 64 cm in the direction of the force. Calculate the work done by

a.    The horizontal component of the force

b.    The vertical component of the force

10. A child tows a toy by means of a string as shown below. The tension in the string is 1.5 N and the string makes an angle of 25 with the horizontal. Calculate the work done in moving the toy horizontally through a distance of 265 cm