You\'re tired of physics teachers telling you that air resistance is too hard to

Question

You're tired of physics teachers telling you that air resistance is too hard to analyze! After all, our world has an atmosphere and if you want to plan out the best way to lob a water balloon at your friend, you're going to have to figure out how to include air resistance. You decide to do an experiment to develop a better understanding of air resistance. You build a spring-loaded catapult that will release a water balloon from essentially ground-level once the spring is fully compressed. You set up a digital video camera so that you can analyze the balloon's trajectory later on a computer. You prepare the balloons so that they all have a mass of 2.5 kg. You shoot several balloons straight up and go home to analyze the video. During a typical trial, the balloon is launched with an initial speed of 20.0 m/s. The balloon reaches a maximum altitude of 13.2 meters. Just before the balloon hits the ground, your video tracking software estimates a final speed of 13.4 m/s. multiple answers possible

A) The overall energy transferred to the air as the balloon rises and falls is 323.4 J.

B) The total source energy stored in the catapult when the spring is fully compressed is approximately 500 J.

C) Your body is about 25% efficient in energy conversion. Setting up the catapult involves burning about 2000 J of your source energy.

D) Peak gravitational potential energy (GPE) including air resistance minus peak GPE without air resistance is about 0 J.

Explanation / Answer

option B and C are correct

(b) total source energy stored in the catapult when the spring is fully compressed = 1/2 mv^2 = 1/2 (2.5)(20)^2 = 500 joules

(c) efficiency= (output energy/ input energy) * 100 = (500/2000)*100 = 25 %

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