Question: You and a friend are entering an egg toss contest. The goal of this contest is to toss an egg the greatest distance without it cracking or breaking open. Describe your strategy for catching eggs that have been thrown a long distance without them breaking in terms of physics. Use terms like impulse and momentum.
Student's Response was:
When trying to catch an egg with the furthest distance, there are several things to keep in mind. Things such as the weight of the egg, the distance you are throwing it, and how you catch the egg can change the results greatly.
First off, when throwing something as small as an egg, one must keep in mind that the further the distance, the more force is exerted into throwing the egg. With more force exerted into the egg, the more momentum there will be. This is especially important when catching the egg, because catching it the wrong way can result in it breaking.
The catching of the egg can be particularly difficult, because the egg is very brittle and fragile. In order to reduce the momentum, you must grab the egg by its sides so it does not splatter on your hand. The egg's impulse which is it's average force over a period of time, must be reduced in order to ensure a safe landing for the egg. By grabbing the egg by the sides, you are reducing it's momentum and impulse to later make the egg fall into your palm.
Tutor's response was: To win the competition, we need to throw the egg as high as we can. So when it fall down, it will have a high velocity as well. Mass of the egg is fixed. So if we need to win this competition, we should be prepared to face a high momentum that we will receive when it come down. Lets say that we take time "t" to catch this egg. So the force while catching the egg will be "F" given by:
F * t = m (vf-vi)
So F = m (vf-vi) / t
And we have already seen that mass m is fixed.
Also Vf = 0 because the egg finally comes to rest after catching.
Vi is the velocity which was there just before catching the egg and we have already seen that, it will be very high if we want to win the competition.
Now, in order to decrease the force, the only thing that we can do is to keep the time of contact with our hands "t" as high as possible.
If we do that we will be able to reduce the force F to such a limit that the egg even though quite brittle, wont break.
To increase the time of contact we need to catch the egg in sweeping action. We need to move our hands downwards so that the relative velocity between the hand and the egg becomes less. This will effectively increase the time "t" and hence the Force F will be reduced.