I was wanting help with my physics post and since no one replied I thought there wasn't a physics tutor on Jiskha, but came back on today cause I really need to get a hang of my physics stuff and luckily seen you Drwls.
A bike rider approachea a hill with a speed of 8.5m/s. The total mass of the bike and rider is 85kg.
A. Find the kinetic energy of the bike and rider.
Formula for Kinetic Energy I got given is...
Ek = 1/2mv62
1/2(85)(8.5)^2
= 3070.6J
^ That was the easy part. But ughh I am hating the second part to it so much.
The rider coasts up the hill. Assuming there is no friction, at what height will the bike come to a stop?
I have no idea what formula to use to solve the question. Formulas I'm given are...
Egp = mgh
Ek = 1/2mv^2
Eh = mcT
Ee = 1/2kx^2
All these formulas are driving me crazy. My teacher with one question did this.. ET = ET'
Ek + Egp = Ek' = Egp
1/2mv^2 + mhg = 1/2mv^2 + mgh
And the mass crosses out for some odd reason. But before we get to this, I seriously need to know meaning of those formulas. Physics is not my strong area, just took this subject because I may need it in the future. But please help.
And the third part to that.
Does your answer depend on the mass of the bike and rider? Explain.
I guess not because there is no friction, but still how would that take away mass? I mean if I were on frictionless ice standing on top of it, my mass wouldn't automatically be erased :\
1 answer
Coasting up the hill, the bike will stop when the initial kinetic energy equals the potential energy increase, M g H. H is the increase in altitude.
Vo^2/2 = g H
Solve for H.
Strictly speaking, the initial kinetic energy is higher because of the rotating wheels, but that additional effect is negligible since the wheels are usually a small fraction of the total weight.