Question

A $3.0N$ force applied on a $0.40kg$ mass makes the mass move at a constant speed of $3.0m{s}^{-1}$, held back by friction. In the span of it moving through $4.0m$, the net work done on the mass is:

• A. $0J$
• B. $0.90J$
• C. $12J$
• D. $-12J$
• E. $-0.90J$

Answer 1

The correct option is A $0J$

As the mass is moving with a constant speed, thus net external force acting on the mass is zero.

$F_{net}=0$

Displacement of the mass

$S=4.0$ m

Net work done on the mass

$W_{net}=F_{net}\times S$

$\Rightarrow W_{net}=0J$