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What amount of force must be applied to 6kg block moving at 13m/s to slow down to 5m/s...

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law222 | Student, Grade 11 | Honors

Posted January 22, 2013 at 4:34 AM via web

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What amount of force must be applied to 6kg block moving at 13m/s to slow down to 5m/s in a distance of 4.5m?The Friction between them is 75N?

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

Posted January 22, 2013 at 5:12 AM (Answer #1)

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We can do this using Newtons second law of motion.

To stop the moving block we have to apply a force against its motion. Both friction and the applied force result in decrease the velocity of the block.

 

Using equations of motion

`V^2 = U^2+2aS`

`a = (V^2-U^2)/(2S)`

`a = (5^2-13^2)/(2xx4.5)`

`a = -16m/s^2`

 

Acceleration is negative because we have a deceleration.

 

Let us say the force is P at the opposite direction to the movement.

Using F = ma to the direction of motion

`-P-75 = 6xx(-16)`

      `P = 21N`

 

So the required external force is 21N at the direction opposite to the movement of block.

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