1. You are daydreaming in class (not Physics, of course!) and remember a game yo
ID: 1316181 • Letter: 1
Question
1. You are daydreaming in class (not Physics, of course!) and remember a game you and a friend used to play when you were little. One of you would get into a plastic laundry basket and the other would pull the basket around on the carpet. You assume the child and the laundry basket together have a mass of 20 kg, and that a force of 60 N is required to start the basket moving. a. With your recently developed physics knowledge, determine the coefficient of static friction between the basket and the carpet. b. If the 60 N force continues, the basket accelerates at 0.97 m/s2. What must be the coefficient of kinetic friction between the carpet and the basket?
2. Three presents are lined up in a row on a frictionless table. Some little kid comes and pushes on the smallest one with a force of 20 N, moving all 3 across the table. The masses of the three presents are 5 kg, 10 kg, 15 kg, in order of placement. a. What is the strength of the force the 10 kg present applies to the 15 kg present? b. What is the strength of the force the 10 kg present applies to the 5 kg present?
Explanation / Answer
fs = us*m*g
us = fs/mg = (60)/(20*9.8) = 0.306
-
b) F = m*a = uk*m*g
uk = a/g = .97/9.8 = 0.09
2)
on 5 kg mass
F - f1 = m1*a
on 10 kg mass
f1 - f2 = m2*a
on 15 kg mass
f2 = m3*a
a = F/(m1+m2+m3)
a = 20/30 = 0.67 m/s^2
f2 = 15*a = 15*(2/3) = 10 m/s^2
F - f1 = 5a
20 -f1 = 3.33
f1 = 16.67 N
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