Question

Urippe Went to start his lawnmower and was having trouble. At the same moment, Uwi was starting her identical lawnmower in the yard next door without any trouble. There was one difference between the two mowers. Urippe's has the starter cord wrapped around a hub 1.35 cm from the center of the flywheel. Uwi's starter cord is wrapped around a hub 10.42 cm from the center of the flywheel. Explain why Urippe is having a harder time pulling his starter cord
In order to start you must reach a minimum of 350 rpm by pulling the starter cord. Determine the angular acceleration in rad/s required to start the lawnmower if it takes 0.294 seconds to pull the starter cord.

What is the acceleration of the pull cord when Uwi starts her lawn mower?

What is the acceleration of the pull cord when Urippe starts his lawnmower?

The rest is on the paper. Thanks so much

Answer 1

Answer:

As each mower presumably needs the same torque to start, and torque is a product of force and moment arm, the longer moment arm of 10.42 cm on Uwi's mower means lower force is required when compared to Urippe's shorter moment arm of 1.35 cm

350 rev/min = 350(2π) / 60 = 36.652 rad/s

36.652 rad/s / 0.294 s = 124.66... 125 rad/s²

a = αR = 125(0.1042) = 12.990... 13 m/s²

a =  αR = 125(0.0135) = 1.68299... 1.7 m/s²

I am GUESSING that we are supposed to model these mowers as a uniform disk

  τ = Iα

FR = (½mr²)α

  F = mr²α/2R

Urippe's pull  = (3.56)(0.2041²)(124.66) / (2(0.0135)) = 702.008... 702 N

Usi's pull =        (3.56)(0.2041²)(124.66) / (2(0.1042)) = 90.9511...91.0 N

L = Iω = (½(3.56)(0.2041²))36.652 = 2.71771...2.72 kg•m²/s  down

using the right hand rule