# A ball with a mass of 0.5 kg is released from rest at a height of 15 meters above ground level. A constant air resistance of 0.9 N acts on the ball. What is the acceleration of the ball and what is...

A ball with a mass of 0.5 kg is released from rest at a height of 15 meters above ground level. A constant air resistance of 0.9 N acts on the ball. What is the acceleration of the ball and what is the speed when it strikes the ground.

Asked on by bberryj99

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted on

A ball with a mass 0.5 kg is released from rest at a height of 15 meters above ground level. Air resistance acts on the ball and is assumed to have a constant value of 0.9 N.

The gravitational acceleration of the ball is 9.8 m/s^2. The deceleration due to the force of air resistance is 0.9/0.5 = 1.8 m/s^2. This gives a net downward acceleration of 9.8 - 1.8 = 8 m/s^2.

As the ball is released from rest the speed with which it hits the ground is v^2 = 2*15*8

=> v = `sqrt 240`

=> `4*sqrt 15` m/s

The ball strikes the ground with a speed of `4*sqrt 15` m/s.

bberryj99 | Student, Grade 10 | eNotes Newbie

Posted on

@qwerty obviously for the question you were supposed to assume that overwise he wouldn't have wrote it

qwerty112358132134 | Student, Grade 9 | (Level 1) eNoter

Posted on

I'm not sure how to solve the math part but you can't assume that air resistance is constant because air resistance increases with speed. A ball moving 1mph will have less air resistance than a ball moving 200mph.

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