Physics
A body is moved in a direction opposite to the direction of force acting on it. State whether the work is done by the force or work is done against the force.
Answer
When a body is moved in a direction opposite to the direction of force then work is done against the force acting on the body.
When the displacement of the body due to application of force is in a direction opposite to the force then,
θ = 180°, and
cos 180° = -1
Therefore, Work done = (-) Force x displacement of the body.
Related Questions
A block of mass 20 kg is pulled up a slope as shown in the figure given below with a constant speed by applying a force of 200 N parallel to the slope from the initial position A to the final position B. Work done in moving the block from A to B is:
- 600 J
- 500 J
- 60 J
- 200 J
A force F acts on a body and displaces it by a distance S in a direction at an angle θ with the direction of force.
(a) Write the expression for the work done by the force.
(b) What should be the angle between force and displacement so that the work done is (i) zero, (ii) maximum?
State whether work is done or not by writing yes or no, in the following cases?
(a) A man pushes a wall.
(b) A coolie stands with a box on his head for 15 min.
(c) A boy climbs up 20 stairs.
Give an example when work done by the force of gravity acting on a body is zero even though the body gets displaced from its initial position.