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Help me with two easy physics questions please

pilebaypilebay Posts: 621Registered User Member
Hey guys my physics homework is due on 9/12 and I need help on these two problems.

1. How long is Tina, a ballerina, in the air when she leaps straight up with a speed of 1.8m/s

2. A Christmas tree ball will break if dropped on a hardwood floor with a speed of 2.0 m/s or more. Holly is decorating her Christmas tree when her cat Trickor, taps a ball, causing it to fall 15 cm from a tree branch to the floor. Does the ball break?

I know that there has to be an easy formula for this but I can't find it. If you can tell me the process by which you get the answer I would be very grateful.
Post edited by pilebay on

Replies to: Help me with two easy physics questions please

  • pilebaypilebay Posts: 621Registered User Member
    I know someone out there knows how to do this. I keep reading about people on this site that get 800's on the SAT II Physics. These questions are really driving me crazy I really really need help.
  • tkm256tkm256 Posts: 1,847Registered User Senior Member
    I'm really awful at this, but I'll try:

    vi= initial velocity (m/s)
    vf= final velocity (m/s)
    a= acceleration (m/s^2)
    t= time (seconds)

    1) For the time going up:
    a = (vf-vi)/t
    -9.8 = (0 - 1.8)/t
    t = 1.8/9.8 = .18, double because she comes down: .367 s

    2) d= (vf^2 - vi^2)/2a
    .15 = (vf^2 - 0)/2(9.8)
    2.94 = vf^2
    vf = 1.71 m/s: the ball does not break

    Big Five equations rock.
  • wrathofgod64wrathofgod64 Posts: 2,217Registered User Senior Member
    a) use the equation v(final) = v(initial) + a*t
    For the time going up
    0 = 1.8 + -9.8*t
    t=.183
    Multiply by two to get total time in the air: .183 * 2 = .367s

    tkm is right for the second one
  • pilebaypilebay Posts: 621Registered User Member
    Thanks so much! I really suck at Physics so I am sure that there will be a lot of posts from me in the coming year.
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