Question

A box of mass 40kg is pushed up a 2m inclined plane.What is the work done by the 250N force when the box reaches the top of inclined plane which is 1m above the ground? a)250J b)400J c)500J d)800J

Answer 1

The work done is 400 J.

Explanation:

By the principle of conservation of energy, the work done equals the increase in gravitational potential energy.

`GPE = m*g*h = 40 kg*9.8 m/s^2*1 m = 392 J ~= 400 J`
(Rounded off to 1 significant digit because of the given data.)

Working it another way just for fun:

The angle between the incline and horizontal is `sin^-1(1/2) = 30^@`.
Therefore the downslope component of the weight, `weight_(ds)`, of the box is

`weight_(ds) = m*g*sin30^@ = (40 kg*9.8 m/s^2)/2 = 196 N`

The work done pushing the box up the incline for 2 m is

`"work" = weight_(ds) * 2 m = 196 N * 2 m = 392 J ~= 400 J`

I hope this helps,
Steve