Question

A man of mass $75kg$ is pushing a heavy box on a flat floor. The coefficient of kinetic and static friction between the floor and the box is $0.20$, and the coefficient of static friction between the mans shoes and the floor is $0.80$. If the man pushes horizontally see figure, what is the maximum mass (in kg) of the box he can move?

• A. $300kg$
• B. $600kg$
• C. $900kg$
• D. none of these

Answer 1

The correct option is A $300kg$

The man can only push as much weight as the friction force provides

$\therefore$ friction force produced by man$=\mu mg=0.8\times 75\times 10=600N$

Friction force between box and floor

$={\mu }^{{}^{\prime }}mg=0.2\times m\times g=2m$

$\Rightarrow 2m=600kg\Rightarrow m=300kg$