# Misc Notes

Created Thursday 05 May 2016

Always make sure formulas are copied down properly.

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Always check for dimensional continuity (I see it as type checking).

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If you throw something up at 10 m/s, when it gets back to the same point while going down it will be at -10m/s.

__This also applies when you're throwing something in an arc. Both the y and x will have the same magnitude on the other end, but maybe negative.__

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If something is thrown towards positive x, and the other is dropped, they will __have the same y value at the same times.__

This also means they will __hit the ground at the same time.__

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If a motorcycle is driving off a cliff and you wanna find out what velocity he's driving at initially in order to hit the ground at a certain x distance,

use the 3rd formula on the y, then use the time with the 4th formula but with x.

This is because we know the acceleration for y, but not for x.

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If a person on a wagon is moving, and throws something upwards, the velocity of the moving wagon will also be added to the velocity.

This might not seem intuitive because air-resistance is neglected.

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If someone is shooting someone with a catapult and the other guy is on a tree and dropping, it will ALWAYS HIT.... given that there is no ground and it's an infinite drop and there's no air resistance.

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A car with a smaller mass will require less force to brake.

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To use Newton's third law, identify the two forces, then ELIMINATE one.

Only one is important because they are both acting on different objects.

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If a box is on the floor of an elevator and the rope snaps, it will remain on the floor.

F=ma

W-N = mg

N=W-mg

=mg -mg

= 0

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Only interested in the force on the object of interest.

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