# Work done on a block

1. May 30, 2010

### thereddevils

1. The problem statement, all variables and given/known data

A wooden block of mass 1.2 kg with dimensions 20cm x 10 cm x 10cm . It's resting on the surface PQYX (with base area 10cm x 10 cm , the vertical side would be 20cm in this case).What is the work done to enable it to rest on surface PQYX

2. Relevant equations

3. The attempt at a solution

On first thought , work done is simply the gain in potential energy ,

mgh=(1.2)(10)(0.2)=2.4 J

but that isn't the answer .

2. May 30, 2010

### tomwilliam

In my understanding, there is no work done if the box is not moving.
You can say that the forces are balanced... that the frictional force acting up the slope is equal in magnitude to the component of the box's weight pointing down the slope, but as Work = (Force) x (distance in direction of the force), my understanding is that no work is done if the box remains steady.

3. May 30, 2010

### tiny-tim

Hi thereddevils!
I don't understand …

is the block tilted? …

and where is the block moving from and to?

4. May 30, 2010

### thereddevils

sorry , i should hv posted the complete question.

Figure 23 shows a wooden block of mass 1.2 kg with dimensions 20cm x 10 cm x 10cm . It's resting on the surface PQRS . What is the workdone to enable it to rest on the surface PQYX ?

PQRS is of base area (20 x 10) and PQXY (10 x10)

THe block is neither moving nor its tilted .

5. May 30, 2010

### tiny-tim

Well, work done is force "dot" displacement …

if nothing has moved, then what's the displacement?