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Inquiry: Ballistic Pendulum

Purpose: To indirectly determine the velocity of a bullet by using a ballistic launcher and a ballistic pendulum.


Sometimes it is not possible to measure the velocity of a bullet directly. If we impact the bullet on an object, we can calculate the velocity by the use of the conservation of energy and momentum laws.

1.) Remove the pendulum. If we shoot the bullets off the edge of a table onto the floor, we can indirectly measure the velocity of the three bullets by measuring the height and the range. Let's use these velocities as the theoretical values.

2.) Attach the pendulum. Derive an equation using the conservation of momentum and energy. Calculate the velocity of the three bullets in terms of the angle and the following constants. Determine percent errors.

  • m(steel) = 8.5 grams

  • m(Al) = 2.8 grams

  • m(Brass) = 9.0 grams

  • m(bob) = 48.8 grams

  • pendulum length = 0.320 meters

Inquiry Questions:

  1. A 10.0 g bullet is fired into a 2.50 kg block of wood at the end of a pendulum which swings to a height of 65.0 cm. How fast was the bullet fired in m/s? (Here you know the height so you do a simpler derivation than the one above.)