Question

Work done by a force on an object is zero, if :

• A. the force is always perpendicular to its acceleration
• B. the object is stationary but the point of application of the force moves on the object
• C. the force is always perpendicular to its velocity
• D. the object moves in such a way that the point of application of the force remains fixed

Answer 1

Answer: (C), (D)

The correct options are
C the force is always perpendicular to its velocity
D the object moves in such a way that the point of application of the force remains fixed

Work done $W=F\cdot dx=F\cdot \frac{dx}{dt}\cdot dt$

Work done by a force on an object is zero, if:

• The force is always perpendicular to its velocity ($\frac{dx}{dt}=0$).
• The object moves in such a way that the point of application of the force remains fixed ($dx=0$).