Sticky Collision

This past Saturday, I watched some football games on TV. This made me think of some sticky collision problems that we did for physics class. The quarterback was scrambling one way and a defensive lineman tackled him from behind in a sticky collision. This meant that the equation m1v1 +m2v2 = (m1 + m2)vf would be very useful to find out an unknown in this problem. For example, if we wanted to find the final velocity if we knew the mass of the quarterback was 100 at a velocity of 4 m/s and the mass of the defensive lineman was 150 at a velocity of 6 m/s, we would just use that equation to solve it.

(100)(4) + (150)(6) = (100 + 150)vf
400 + 900 = 250vf
vf = 5.2 m/s

Space Needle

This past summer, I went to Seattle, WA and had the opportunity to stand on the observation deck of the Space Needle. This structure is very tall. I didn't know it back then but there is a lot of physics involved in this marvel.

The potential energy of me standing on that observation deck was very big. Using the potential energy formula, PE = mgh, where m = mass (kg), g = gravitational pull, and h = height (m), I could tell that the potential energy was going to be high since g = 9.8 and h = 160 m. If I knew my mass in kg I would tell you the exact amount of potential energy I had but I can't. Nevermind. I found out how to convert my weight into kg. Well, since I am 59 kg, my potential energy is 92,512 J (59 x 9.8 x 160).

Suppose I felt like falling off the Space Needle. My kinetic energy would be very big, too. In fact, at the moment I would hit the ground I would have the same amount of kinetic energy as I had potential energy at the top of the observation deck since energy cannot just disappear or suddenly be added. Instead it changes from potential to kinetic energy.

Since KE = 1/2 mv^2, and KE at the bottom = PE at the top, I was also able to find out that the speed at which I would hit the ground would be 56 m/s if there were no air resistance. Falling from this height would be very painful.