Finding Work given mass and distance

[MisterFusion]

Homework Statement

How much work is required to lift a 4.0 kg concreted block to a height of 2.0 m?

mass = 4.0 kg
distance = 2.0 m

Homework Equations

W = Fd
F = mg (not sure if this is used)

The Attempt at a Solution

To find Force, I used the formula F(orce) = m(***) times g(ravity) which would be F=(4.0kg)(9.8m/s²), giving me F=39.2N
Now, I used this information in the W = Fd equation, giving me W = (39.2N)(2.0m) = 78.4 J

The reason I am unsure if this is correct is that an example is given with a very similar problem:
m=5.0kg
d=0.45m (above the counter)

The answer given is 3.22 J. Using the formulas I used, I come up with 22.05 J.

 

[PhanthomJay]

Your answer looks OK...is the 'similar' problem exactly similar??

 

[MisterFusion]

It is exactly similar. The wording is this:

A 5.0 "kilo" bag of sugar is on a counter. How much work is required to put the bag on a shelf a distance of 0.45m above the counter?

The answer given is 3.22 J

That really made me think my answer is wrong, but I suppose the book could be wrong - I wanted to run it by some experts to be sure.

 

[PhanthomJay]

That's a hefty bag of sugar, must be for a restaurant chain since it's about twice the weight of what I buy in the supermarket. Or maybe its from BJ's or one of those wholesale outfits where sizes are double or triple or more the supermarket size. Anyway, their answer doesn't make sense. Welcome to PF!