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A small object, of mass 0·02kg at the top of a building 160 m high, is dropped from...

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saj-94 | (Level 1) Salutatorian

Posted July 28, 2013 at 11:24 AM via web

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A small object, of mass 0·02kg at the top of a building 160 m high, is dropped from rest.

(a) Ignoring air resistance, calculate

  1. the speed of the object as it hits the ground and the time taken for the object to reach the ground.

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jeew-m | College Teacher | (Level 1) Educator Emeritus

Posted July 28, 2013 at 11:33 AM (Answer #1)

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We can use the equations of motion here.

`darrV^2 = U^2+2aS`

`V = ?`

`U = 0` as it is dropped.

`a = 9.81m/s^2`

`S = 160m`

`V^2 = 0+2xx9.81xx160`

`V^2 = 3139.2`

`V = 56.03m/s`

Using `darrV = U+at`

`t = (V-U)/a`

`t = (56.03-0)/9.81`

`t = 5.71s`

So when the ball hit the ground the velocity will be 56.03 and 5.71 seconds will be the time taken.

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