Physics
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?
Answer
(a) When force acts at an angle θ to the direction of displacement then work done is
W = F × S Cos θ
(b)
(i) For work done to be zero the angle between force and displacement should be equal to 90° as cos 90° = 0
Therefore, product will also be zero.
W = F × S Cos 90°
= 0
(ii) For work done to be maximum the angle between force and displacement should be equal to 0° as cos 0° = 1
Therefore, product will also be maximum.
W = F × S Cos 0°
= F × S
Related Questions
Assertion (A): When the displacement is normal to the direction of force, the work done is zero.
Reason (R): Work done depends on the angle between force and displacement.
- Both A and R are true and R is the correct explanation of A
- Both A and R are true but R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Assertion (A): Work done by frictional force is negative.
Reason (R): This is because frictional force acts along the direction of motion.
- Both A and R are true and R is the correct explanation of A
- Both A and R are true and R is not the correct explanation of A
- Assertion is false but reason is true
- Assertion is true but reason is false
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.
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.