Kelli weighs 420N, and she is sitting on a playground swingseat that hangs 0.40m

Question

Kelli weighs 420N, and she is sitting on a playground swingseat that hangs 0.40m above the ground. Tom pulls the swing backand releases it when the seat is 1.00m above the ground. a) How fast is Kelli moving when the swing passes through itslowest position? b) if Kelli moves through the lowest point at 2.0m/s, how muchwork was done on the swing by friction? Kelli weighs 420N, and she is sitting on a playground swingseat that hangs 0.40m above the ground. Tom pulls the swing backand releases it when the seat is 1.00m above the ground. a) How fast is Kelli moving when the swing passes through itslowest position? b) if Kelli moves through the lowest point at 2.0m/s, how muchwork was done on the swing by friction?

Explanation / Answer

Kelli weighs 420N, and she is sitting on a playground swingseat that hangs 0.40m above the ground. Tom pulls the swing backand releases it when the seat is 1.00m above the ground. a) How fast is Kelli moving when the swing passes through itslowest position? b) if Kelli moves through the lowest point at 2.0m/s, how muchwork was done on the swing by friction?

part a)
when she is crossing mean position
total potential energy=kinetic energy
mgh=1/2mv2
v=2gh=2*9.8*1=4.427m/sec


part b)

if there is no friction
work done =1/2mv2=1/2*420/9.8*19.6=420J
in the presence of friction the workdone=1/2mv2=1/2*420/9.8*4=85.71J
so work done by friction=420-85.71=334.29J

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