Question

A block weighing 15 newtons is pulled to the top of an incline that is 0.20 meter above the ground, as shown below. if 4.0 joules of work are needed to pull the block the full length of the incline, how much work is done against friction?

Answer 1

Total work done here against two forces

1. Work done against gravity

2. work done against friction

Here work done against gravity is given by

$W_g = mgH$

here we know that weight of the block will be

$Weight = mg = 15 N$

$H = 0.20 m$

$W_g = 15(0.20) = 3J$

now we will say

$W_{total} = W_{friction} + W_g$

as we know that total work

$W_{total} = 4J$

$4 = 3 + W_{friction}$

$W_{friction} = 4 - 3 = 1J$

so work done against friction is 1 J