A body of man 100 kg travelled 10 m before coming to rest. If μ = 0.4, work done against friction is (motion is happening on horizontal surface, take g = 10 m/s²)

To find the work done against friction, we need to analyze the forces acting on the body moving along the horizontal surface.

First, let's identify the given values:
Mass of the body, $m=100\text{kg}$
Distance travelled, $d=10\text{m}$
Coefficient of friction, $\mu =0.4$
Acceleration due to gravity, $g=10{\text{m/s}}^2$

Since the motion is happening on a horizontal surface, the normal force ($N$) acting on the body balances its weight:
$N=m\cdot g$

Substituting the given values:
$N=100\text{kg}\cdot 10{\text{m/s}}^2=1000\text{N}$

The frictional force ($f$) resisting the motion is given by:
$f=\mu \cdot N$

Substituting the values of $\mu$ and $N$:
$f=0.4\cdot 1000\text{N}=400\text{N}$

The work done against friction ($W$) is equal to the product of the frictional force and the distance travelled:
$W=f\cdot d$

Substituting the values:
$W=400\text{N}\cdot 10\text{m}=4000\text{J}$

Therefore, the work done against friction is 4000 J.