May-7-2015 Lab 15: Inelastic Collision

Purpose :  work out the initial speed of the small ball and its speed of uncertainty by using a small ball to hit the holder from the machine which like the picture.

set up:


Using this machine, we could give the small ball a initial speed, and the holder will hold the ball (which means they will stick together) when the ball hit the holder .  In addition, there is a red rod that will show us the highest position and angle of the holder.

After we collect all of data we need, we could calculate the initial speed of the ball by Laws of conservation of momentum and energy conservation.



Put the holder at the initial position, and put ball into the machine. then push the button, the ball will shoot out and hit the holder.

there is the graph after the ball and holder stick together, and the data we measured:

we measured the mass of ball M(ball) = 7.63 g +- 0.1 g

M(block) = 80.9 g +- 0.1 g

the changing degree of the holder:     θ = 17.5 degrees +- 0.5 degrees

the length of the string L = 0.201 m +- 0.001 m







after the ball and holder stick together, the velocity will change. so we need to know the velocity when ball and holder stick V(total) which we could calculated it by using law of  energy conservation,  Then we could know the initial speed of the ball V(ball) of ball by using law of momentum conservation.  Here is calculation:  

there is calculation to find ball's uncertainty of initial speed:

Conclusion :

For this lab, we measured the length of string, mass of ball and holder, and we collected the changing of degree of the holder after we shot the ball. Then we used the laws of conservation of momentum and energy conservation to work out the initial speed of the ball is 4.9545 m/s, and its uncertainty is only 3.22%. that's mean Our result is pretty good.