Question

A boy pulls a $5kg$ block along a $20m$ long horizontal surface at a constant velocity by applying a horizontal force $F$. If the coefficient of kinetic friction is $0.2$, how much work does the boy do on the block? ($g=10m{s}^{-2}$)

• A. $100J$
• B. $300J$
• C. $200J$
• D. $400J$

Answer 1

Answer: (C)

$200J$

Given , $m=5kg,d=20m,\mu =0.2,g=10m/s^2$

As the block moves with a constant velocity , therefore net force on block is zero .

Force applied by boy = force applied by friction

$F=\mu R=\mu mg$

or $F=0.2\times 5\times 10=10N$

Hence , work done by boy ,

$W=Fd$

or $W=10\times 20=200J$