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Whos a physics genius? Two questions regarding Work/Energy

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  • replied
    oopsie...slight mistake there, missed the equation and the problem b/c i didn't read close enough

    Power = Work / Time ( i mistated the equation for work earlier); Work = Force * Distance

    so....

    Total mass = 4 * 65 kg = 260 kg

    Force = 260 kg * 9.81m/s^2 = ~2551 N

    Work = 2551N *140 m = 357140 N*m

    Power = 357140 N*m / 120 seconds
    =2976 N*m/s or ~3000 W ( 1 watt = 1 N*m/s)




    <<edit>> i see now that -ORC-P has already answered the question...so nevermind.<<edit>>

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  • replied
    Originally posted by vaxopy
    The answers are

    1) 40.8kg
    2)3.0 × 10^3 W

    so far no one has been right

    anyone know how to get these answers based on the question?
    Wow, maybe that is telling you something. Go to a physics forum. Use google to find one. They exist I am sure.

    Leave a comment:


  • replied
    Well, cos(60) is .5

    So, the tension in the vertical direction is actually 400N.

    Remember, F=ma, so 400 = m * 9.8 (<-- acceleration of gravity). So 400/9.8 = 40.8 kg.


    For the ski lift, the work done is independent of the path taken, and it's mgh (the potential energy).

    So mgh for each skier is 65 * 9.8 *140 = 89180.

    Multiply that out for 4 skiers and it's 356720.

    Now Power = work/time, and the time is 120 seconds.

    356720/120 = 2972.67 = 2.972 x 10^3 ~ 3.0 x 10^3 Watts.

    Hope that helps

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  • replied
    Maximum force on the rope is in vertical position so the calculation is for that spot.

    (1) F=Fg+Fcp=mg+mv^2/r=800N max

    Preservation of energy: g=10m/s^2
    (2) mgh=mv^2/2

    Geometry: h - height of the mas in rest.
    (3) cos60=(r-h)/r ---> h=r(1-cos60)

    (3)--->(2)

    (4) mgr(1-cos60)=mv^2/2 ---> v^2/r=2g(1-cos60)

    (4)--->(1)

    mg+m2g(1-cos60)=800N --->m=800/(((1+2(1-cos60))g)=40Kg

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  • replied
    are you pop quizing us?

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  • replied
    The answers are

    1) 40.8kg
    2)3.0 × 10^3 W

    so far no one has been right

    anyone know how to get these answers based on the question?

    Leave a comment:


  • replied
    I took AP Physics last year, but I forget a lot of the stuff. For the rope... don't you need length, or something also? I am pretty sure it depends how long it is.

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  • replied
    A swing is made from a rope that will tolerate a maximum tension of 800N without breaking. Initially, the swing hangs vertically. The swing is then pulled back at an angle of 60.0° with respect to the vertical and released from rest. What is the mass of the heaviest person who can ride the swing?

    In 2.0 minutes, a ski lift raises four skiers at constant speed to a height of 140 m. The average mass of each skier is 65 kg. What is the average power provided by the tension in the cable pulling the lift?
    2 weeks

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  • replied
    i dont' wanna get out no paper to figure out teh swing problem...but the ski lift should be:

    Work = force * distance / time

    so work = (65kg * 9.81 m/s^2) * 140 m / 120 sec

    work = ~744 N*m/s

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  • replied

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  • replied
    You’re better off going to the Ask Jeeves forum or something. I just did a search on your nick, and out of your 16 posts in this community only 4 of them were on-topic. This isn’t the place to ask for help on homework.

    Leave a comment:


  • replied
    Originally posted by Mr. Brownstone
    A train sets off for New Orleans from San Antonio at 14:00 and accelerates to 70 MPH. Vaxopy starts off from New Orleans at 14:30 and runs along the tracks towards San Antonio at 7 MPH. How long does he have left to live?
    Originally posted by If you see kay
    stop sleeping in class
    if you have questions ask your teacher,dont just ask ppl to answer them for you.
    an "I dont know" would suffice =)

    Leave a comment:


  • replied
    A train sets off for New Orleans from San Antonio at 14:00 and accelerates to 70 MPH. Vaxopy starts off from New Orleans at 14:30 and runs along the tracks towards San Antonio at 7 MPH. How long does he have left to live?

    Leave a comment:


  • replied
    stop sleeping in class
    if you have questions ask your teacher,dont just ask ppl to answer them for you.

    Leave a comment:


  • replied
    Re: Re: Whos a physics genius? Two questions regarding Work/Energy

    Originally posted by willhaven
    depends on the maximum tension of the rope
    800N - question fixed

    Leave a comment:

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