Question

A body of mass $40$ kg is dragged $8$ meter on a rough horizontal surface in $10$ with a constant velocity by a constant force of $20$ N, then calculate the work done by the force and total work done by all the forces.

Answer 1

$M=40kg$ $F=20N$ $t=10s$

Friction force $=\mu mg=0.2\ast 40\ast 10=80N$

Net force in forward direction $=20-80=60N$

So acceleration $=a=Force/m=60/2=30m/s²$

Initial speed $=u=0$

Distance traveled $=s=ut+1/2at²=0+1/2\ast 30\ast 10²=0.000166m$

Work done by $F=F\ast s=20\ast 0.00016=0.0032kJ$

Work done by Friction force $=-30\ast 0.0032=-0.096kJ$ (heat dissipated)

The kinetic energy of the body $=1/2mv²=1/2m\left(2as\right)$

$=2\ast 30\ast 0.00016=0.0096kJ$