A 2.4 kg purse is dropped from the top of the Leaning Tower of Pisa and falls 55 m before reaching the ground with a speed of 30 m/s. What was the average force of air resistance?
2007-03-10 09:38:01 · 2 answers · asked by Jessie L 2 in Science & Mathematics ➔ Physics
The total work done on the purse (by gravity) is
mgh = 2.4*9.8*55 = 1293.6J
The total KE of the purse when it hits the ground is
mv²/2 = 2.4*30²/2 = 1080J so the total work done by air resistance is
1293.6 - 1080 = 213.6J Since work is force through a distance, the total work done (for a constant, 'average' force) is
213.6 = F*55 => F = 3.884 N
HTH ☺
Doug
2007-03-10 09:51:02 · answer #1 · answered by doug_donaghue 7 · 2⤊ 0⤋
Without air resistance the speed would have been 32.833 m/s.
The time of the actual fall = âh/Vave = 55/15 = 3.666sec
So, the average wind force is Fw = mâV/ât = 2.4*2.833/3.666 = 1.855 N
2007-03-10 17:54:37 · answer #2 · answered by Steve 7 · 0⤊ 2⤋