(a) A father pulls his young daughter on a sled with a constant velocity on a le
ID: 1778639 • Letter: #
Question
(a) A father pulls his young daughter on a sled with a constant velocity on a level surface a distance of 10m as shown below. If the total mass of the sled and the girl is 70 kg and the coefficient of kinetic friction between the sled runners and the snow is 0.20. How much work does the father do? [ Select ] (b) How much work does the father do if the father pushed horizontally on his daughter's sled to move it up a snowy incline as shown below in part (b) [Select ] 30° 3.6 m 15° O 2010 Pearson Education, IncExplanation / Answer
(A) Work done = F.d = F d cos(theta)
in horizontal, F cos30 - f = 0
f = uk N = uk (mg - Fsin30)
F cos30 - 0.20 x 70 x 9.8 + 0.20 F sin30 = 0
F = 142 N
W = 142 x 10 x cos30 = 1230 J
(B) net work done = change in KE
work done by father + work done by gravity = 0
W = - (- 70 x 9.8 x 3.6) = 2469.6 J
4. W = k x^2 /2 = 1000 (0.10^2) /2
W = 5 J
(b) W = 1000 (0.20^2 - 0.10^2) /2
= 15 J
(c) W = 1000 (0.30^2 - 0.20^2) / 2
W = 25 J
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