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Old Nov 9th 2009, 01:32 PM   #1
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velocity of a bullet

a 15g bullet is fired horizontally into a 3kg block hanging from a string,the bullet sticks into the block. What is the velocity of the bullet if it cause the block to move 10cm above its initial level? I used formula 2gh were g is 10m/s and h is 10. It gave me 200m/s and the square root of that is 14.4ms
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Old Nov 10th 2009, 01:05 AM   #2
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A similar problem has been recently solved where a ballistic pendulum is mentioned. Do look it up.

Firstly convert all values into proper units.

The increase in p.e. of the bullet + block = their initial K.E.

(M+m) g h = 0.5 (M+m) V^2. Find V.

Since the bullet sticks to the block the collision is inelastic i.e. the K.E. is not conserved.

So we use consevation of momentum. The initial momentum of the bullet must be equal to the final momentum of the block + bullet.

Thus,

m v = (M+m)V . Find v
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