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Lab 15- Ballistic collision

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Purpose:
Determine the firing speed of a ball from a spring-loaded gun.
Introduction:
In this ballistic pendulum lab, a ball is fired into a nylon block, which is supported by four vertical strings. The ball is captured by the block and they rise together through some angle. Use the equipment find out the angle. The kinetic energy of the system including block and ball transfers into gravitational potential energy during this process. So by measuring the angle we can derive the initial kinetic energy and finally, the speed.

Procedure:
First measure and record the mass of the ball and the block. Then set the ballistic pendulum up as following.
After setting up, level the apparatus and the block. After all preparation done, pull back and lock the spring into position. Zero the angle indicator. Then put the ball into position. Then fire the ball into the block and record the maximum angle. Repeat these steps by four to five times to get a reliable average value.

Calculating:
In this lab we actually did five trials to make sure the result is reliable. Here is data determined 


This speed is much smaller than the calculation result. This condition may be due to the air resistance, which will decrease the speed when the ball is flying. Error may also come from the way we get our average value or the angles.

Conclusion:

In this lab we learned to calculate the initial firing speed of a ball from a spring-loaded gun with a ballistic pendulum. Then we verify the speed by calculating it with a horizontal projectile motion. There is a quite large error caused by air resistance. But besides air resistance, I think the Θ3 may be too larger than the other angles, which can result the error, too. 

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