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Homework Help: Kinematics questions

  1. Oct 10, 2009 #1
    1.A stone is thrown vertically upward with a speed of 11.0 m/s from the edge of a cliff 79.0 m high (Fig. 2-32).

    (a) How much later does it reach the bottom of the cliff?

    (b) What is its speed just before hitting?

    (c) What total distance did it travel?

    2.If a car rolls gently (v0 = 0) off a vertical cliff, how long does it take it to reach 74 km/h?

    3.A sports car accelerates from rest to 99 km/h in 6.2 s. What is its average acceleration in m/s2?
  2. jcsd
  3. Oct 10, 2009 #2
    Most of these can be solved once you set up an equation of motion representing your situation.

    I suggest you make an attempt :eek:
  4. Oct 10, 2009 #3
    yes i figured out the last two but the first one i am having trouble on... I found most of the missing variable but i cant seem to get the ones i need right.
  5. Oct 11, 2009 #4
    the answers i have gotten for the first one is
    A) 5.12
    Can someone tell me if i did this wrong and help me
  6. Oct 11, 2009 #5
    a) 0.13424051
  7. Oct 11, 2009 #6
    a) 0.13424051s doesn't leave much time to reach the maximum height and then fall 79m plus the additional height achieved by the 11.0m/s initial velocity.
    b) Accelerating to 588.495976m/s in 0.13424051s would require that acceleration due to the force of gravity is 4380.1979 m/s2
    c) What about the distance upward due to the initial velocity of 11.0m/s?
  8. Oct 11, 2009 #7
    I came up with
    a) 5.29 s
    b) 40.9 m/s (the problem asks for speed, which is the absolute value of velocity)
    c) 91.4 m
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