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ball thrown vertically upwards physics?

a ball thrown vertically upwards from a bridge that is 40m above ground. The ball strikes ground in 4 seconds. What is speed at which ball was thrown upwards, and at what speed will ball hit ground?

Iv been stuck for a long time please any help will help.

2 Answers

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  • 10 years ago
    Favorite Answer

    With the displacement formula (x = v0 *t + (1/2) a t^2), you have all the values except the unknown initial velocity. So solve for that.

    x = v0 t + (1/2) a t^2

    v0 t = x - (1/2) a t^2

    v0 = (x - .5 a t^2) / t

    v0 = (40m - .5 (9.81m/s^2) (4s)^2) / 4s

    v0 = (40m - .5 (9.81 m/s^2) (16s^2)) / 4s

    v0 = (40m - 78.5m) / 4s

    v0 = -38.5m / 4s

    v0 = -9.6 m/s

    Since gravitational acceleration is downward (and positive), the negative initial velocity implies an upward direction.

    v = v0 + a t

    v = -9.6m/s + 9.81m/s^2 * 4s

    v = -9.6m/s + 39.24 m/s

    v = 29.6 m/s

  • 10 years ago

    1/2 A T^2 = distance, so 3 sec = 45 m &(30 m/s) down, up at 10m/s should stop in one meter with 5 meter displ.

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