physics questions 3?

A foul ball is hit straight up into the air with a speed of about 31 m/s.

(a) How high does it go?

___ m

(b) How long is it in the air?

___s

A helicopter is ascending vertically with a speed of 8.00 m/s. At a height of 135 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground?

___ s

stone is thrown vertically upward with a speed of 14.5 m/s from the edge of a cliff 62.0 m high (Fig. 2-32).

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

__ s

(b) What is its speed just before hitting?

___ m/s

(c) What total distance did it travel?

___ m

A 90 m long train begins uniform acceleration from rest. The front of the train has a speed of 21 m/s when it passes a railway worker who is standing 172 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2-36.)

____m/s

1 Answer

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  • 1 decade ago
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    1st question

    use d = 1/2 a t^2 + vt

    and v = at + v0

    Here v0 = 31m/s and a = -9.8m/s^2, the ball will be highest when it reaches the apex where v = 0 so

    0 = -9.8 t + 31

    t = 31/9.8 = 3.16 s

    At this time it will have reached a distance of

    d = 1/2 (-9.8) (3.16)^2 + (3.16)(31) = 44.06 m

    It will be in the air for 3.16s*2 = 6.32s

    Second question

    again d = 1/2 a t^2 + vt

    -135 = 1/2 (-9.8) t^2 + 8 (t)

    0 = -4.9 t^2 + 8t + 135

    solve for t

    t = 6.13 s

    Use the same formulas for the other two questions and you should be ok.

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