Shouldn't the slopped distance be considered instead of the height?
(Sayonara Zetsubou Sensei: chapter 233)
Not quite, you have to multiply distance by the force applied to the object (its weight in Newtons), but they're using its mass (kilograms).
It's actually 98 Nm, since weight = mass * gravitational acceleration and g ≈ 9.8 m/s² (you'll see people give more digits but it actually varies by at most 0.1 m/s² or so depending on where you are).