e ult ew History Bookmarks Window Help HW 10 “ mechanics Student Center rd O 2/4
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e ult ew History Bookmarks Window Help HW 10 “ mechanics Student Center rd O 2/4 points Answers CJ10 6.P.051 A projectile of mass 1.150 kg is shot straight up with an initial speed of 27.0 m/s (a) How high would it go if there were no air resistance? 37.2 (b) If the projectile rises to a maximum height of only 29.0 m, determine the magnitude of the average force due to air resistance 92.345 Additional Materials section 6.6 My Notes O Ask Your Te 0/4 points | Previous Answers CJ10 6.P053 Starting from rest, a 91-kg firefighter slides down a fire pole. The average frictional force exerted on him by the pole ha magnitude of 820 N, and his speed at the bottom of the pole is 3.0 m/s. How far did he slide down the pole? 7.75Explanation / Answer
System: the object and the earth:
Work done by air resistance = delta E = delta K + delta Ug
F*h*cos180degrees = K(final) - K(initial) + Ug(final) - Ug(initial)
(180degrees since the air resistance is in opposite direction w/ the motion upward of the object)
K(final) = 0 since the object stops at the max height
U(initial) = 0 ( choose Ug=0 at the starting point)
---> - F*h = - 1/2*m*v^2 + mgh
F = [1/2*m*v^2 - mgh]/h = (1/2*1.15*27^2 - 1.15*9.8*29)/29 = 3.18 N
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