Question

A block of mass $M$ is hanging over a smooth and light pulley through a light string. The other end of the string is pulled by a constant force $F$. The kinetic energy of the block increases by $40$ $J$ in $1$ $s$. The tension in the string is:

• A. $F$
• B. $Mg$
• C. $F+Mg$
• D. $F-Mg$

Answer 1

The correct option is A $F$

Since a force $F$ is pulling the string, the tension in the string is $F$.
However the forces acting on the block are tension$=F$ upwards and weight$=Mg$ downwards and thus has a net acceleration upwards.