Wednesday, November 11, 2009

Projectile Motion: When Water Balloons Fly

Projectile Motion

One day, I was walking home from school when suddenly I heard a loud smack behind me. I turned around to discover that a water balloon had hit the pavement. Then, trying to find out what direction the balloon came from, I saw another and ran to avoid being soaked. As I looked at the direction it came from, I saw a small group of 4 or 5 people with a water balloon launcher and a huge bucket filled with the balloons. I saw them pull back the launcher and one yelled “PULL!” and I saw the balloon approaching with great speed. I was terrified and began to sprint when my jacket caught onto the fence next to me and I was stuck. I was terrified and anxious on whether I would get hit because I was a sitting duck. The balloon barely missed me. Unfortunately, I was still stuck and they had already loaded another balloon. I knew that there was only one way to find out how much time I had to escape the fence was PHYSICS! Fortunately, I had Physics class that day and we had just learned about projectile motion. I remembered that I could find how long the projectile, in this case a speeding water balloon, was in the air. I knew that their last miss would have been a direct hit if they had aimed right and saw that the launcher was at the same angle. I would have to base how much time I had left on the last shot. I could tell that I was about 24m from where the balloons were being launched and that it was being launched at an angle of about 15m/s at 45˚ in relation to the horizontal. I quickly thought through all the ways that I could calculate the time: t = x/Vocosθ or t = Vosinθ/g. Knowing what I was given I quickly decided the fastest way was t = x/Vocosθ. So I plugged in the distance, x = 24m, divided by Vo = 15m/s*cos45˚ which all came out to 2.3s. Once I heard them shout “PULL!” again, I knew I needed to act fast. Finally I broke free from the fence and sprinted away dodging the water balloon at the last second all because of PHYSICS!

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