Question

A block of mass m slides along the track with kinetic friction $\mu$. A man pulls the block through a rope which makes an angle $\theta$ with the horizontal as shown in the figure. The block moves with constant speed V. Power delivered by man is :

• A. $TV$
• B. $TVcos\theta$
• C. $(Tcos\theta -\mu mg)V$
• D. Zero

Answer 1

The correct option is B $TVcos\theta$

The body is moving with constant speed, so the work is done by the horizontal component of the force.
Horizontal component is $Tcos\theta$
$Power=Force\times speed=Tcos\theta \left(V\right)=TVcos\theta$