Question

A particle is moving in a circular path of radius $r$ under the action of a force $F .$ If at an instant velocity of particle is $v$, and speed of particle is increasing, then

• A. $\vec{F} \cdot \vec{v}=0$
• B. $\vec{F} \cdot \vec{v} > 0$
• C. $\vec{F} \cdot \vec{v} < 0$
• D. $\vec{F} \cdot \vec{v} \geq 0$

Answer 1

Answer: (B)

Net force will be in the direction of net acceleration.
Here accelerations are of two types
(i) Centripetal
(ii) Tangential
$\theta<90^{\circ}$ always
$\Rightarrow \vec{F} \cdot \vec{v}>0$