p08_004.pdf

4. We use Eq. 7-12 for W g and Eq. 8-9 for U .

(a) The displacement between the initial point and A is horizontal, so φ =90 ◦ and W g = 0 (since

cos90 ◦ =0).

(b) The displacement between the initial point and B has a vertical component of h/ 2downward(same

direction as F g ), so we obtain W g = F g ·

d = mgh .

(d) With the reference position at C ,weobtain U B = mgh/ 2.

(e) Similarly, we ﬁnd U A = mgh .

(f) All the answers are proportional to the mass of the object. If the mass is doubled, all answers are

doubled.

d = mgh/ 2.

direction as F g ), so we obtain W g = F g ·