Work
- Work done by a constant force is given by the product of the force and the distance moved in the direction of the force.
- The unit of Nm(Newton metre) or J(Joule).
- Work is a scalar quantity.
Formula
When the direction of force and motion are same, θ = 0o, therefore cosθ = 1
Work done,
W = F × s
Example:
A force of 50 N acts on the block at the angle shown in the diagram. The block moves a horizontal distance of 3.0 m. Calculate the work being done by the force.
Answer
Work done,
W = F × s × cos θ
W = 50 × 3.0 × cos30o = 129.9J
A force of 50 N acts on the block at the angle shown in the diagram. The block moves a horizontal distance of 3.0 m. Calculate the work being done by the force.
Answer
Work done,
W = F × s × cos θ
W = 50 × 3.0 × cos30o = 129.9J
Example:
The diagram above shows a 10N force is pulling a metal. The friction between the block and the floor is 5N. If the distance travelled by the metal block is 2m, find
- the work done by the pulling force
- the work done by the frictional force
Answer:
(a) The force is in the same direction as the motion. Work done by the pulling force,
W = F × s
W = (10)(2) = 20J
(b) The force is not in the same direction of motion, work done by the frictional force
W = F × s × cos180o
W = (5)(2)(-1) = -10J
