# Concept of Net Work Done

No work is done by a force on an object if the force is always perpendicular to its acceleration. True or False

According to me, it is true. But the answer was given False.

If you consider an accelerated circular motion. The centripetal force is perpendicular to the tangential acceleration of the object. Yet the work by it remains zero. So it should be true. Can anyone explain?

• Your example is not correct. In the case of uniform circular motion both the force and the acceleration point inwards towards the center of the circle. Thus they are parallel, and sure not perpendicular to each other. In this case the work is zero because the force is perpendicular to the velocity. – eranreches Nov 12 '17 at 17:37
• The statement as you've written it is plainly impossible - Newton's second law $\vec F = m\vec a$ tells you that force and acceleration are always parallel and cannot be perpendicular. If you've mistranscribed the statement and it originally reads that the force is perpendicular to the velocity, then yes, the statement is true. – Emilio Pisanty Nov 12 '17 at 17:37
• I am talking about "accelerated circular motion", not uniform circular motion. In which object has two accelerations perpendicular to each other. – Piano Land Nov 12 '17 at 17:56