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Monday, October 24, 2011

Q.361. Conservation of momentum and energy

Question 361.
An 8.0 g bullet is fired into a 4.0 kg ballistic pendulum and becomes embedded in it. If the pendulum rises a vertical distance of 10.0 cm, calculate the initial speed of the bullet.


Answer 361.
When the bullet is embedded in the pendulum, linear momentum is conserved.

=> (0.008) u + 0 = (4.008) v ... ( 1 )
where v = velocity of pendulum with embedded bullet

Also, the kinetic energy of the pendulum with bullet is converted into potential energy
=> (1/2) (4.008) v^2 = (4.008) * (9.81) * 0.10
=> v^2 = 1.962
=> v = 1.4 m/s

Plugging this value of v in eqn. ( 1 ),
velocity of the bullet, u
= 1.40 * (4.008)/(0.008) m/s
= 701.4 m/s.

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