Question

The work w done when lifting an object varies jointly with the object's mass m and the height h that the object is lifted. the work done when a 120-kilogram object is lifted 1.8 meters is 2116.8 joules. how much work is done when lifting a 100-kilogram object 1.4 meters

Answer 1

Work done can be computed using the formula:

$W=Fd$

Where:

W = work (J)
F = Force (N)
d = Distance (d)

Looking at the given, you know that you do not have a value for force, so you will have to solve for it. 

$F = ma$

Where:

F = Force
m = mass
a = acceleration

Because the object is being lifted, the acceleration will rely on gravity. Acceleration due to gravity is a constant 9.8 m/s^2. Let's list our given first:

F = ?
m = 100kg
a = 9.8m/s^2

Put that into our equation and solve:
$F=ma$
$F=(100kg)(9.8m/s^{2})$
$F=980kg.m/s^{2}$

Our force is then 980 N. 

Now that we have force we can solve for Work. The given for work is as follows:
F= 980N
d = 1.4m

Put that into our formula and solve:
$W = Fd$
$W = (980N)(1.4m)$
$W = 1,372J$

The work done is 1,372J.