Recent content by localrob

Thanks for the replies, I didn't know that small amount of localized charges could be transferred or about the water on the pith balls.

A negatively charged plastic rod will negatively charge a pith ball when in contact. My understanding is that the extra electrons transfer from the rod to the ball, thus giving the pith ball a negative charge. When an electrophorus is charged and the metal pan is put on top, it doesn't become...

That's how I feel too. I did see a post on these forums where someone found the formula to be 2/3mr^2, but I don't know where that came from.

I think that for a high school physics problem, it can be assumed to act like a rod. So when finding the rotational kinetic energy of a spinning propeller, I could use the rod formula. But I was curious if there were another generally accepted formula for a propeller that I could use. I'm not...

Is there a moment of inertia formula for a 2 bladed propeller? If you only have the mass and the length of the propeller, I would think a good estimate would be using a rod rotating about the middle. 1/12ml2

That really cleared things up for me, thanks a million.

Maybe looking at this with the ship moving toward the observer isn't the best way. Let me propose a modified problem. Lets say a stationary observer watches a ship fly from the sun to the Earth at 0.5c. a) Since it would normally take light 8 min to get to Earth, the observer would see the...

Yes that makes sense. Thanks.

1) During his flight, his clock would tick normally though, right? So wouldn't it appear to him that he has traveled for 16min but to observers it appears he's traveled for longer? I mean, both clocks in their own reference frames would be ticking normally. Once he decelerates and lands they...

Sorry for yet another time dilation question. I have a couple example problems that I can't seem to explain. 1) A ship leaves the Sun and heads for Earth at 0.5c. An observer on Earth would see the the light from the sun take 8 min, and the ship take 16 min. The pilot's clock would show it...

reaction time is a time, that's all. What do you know about velocity? Do you have a formula or definition for it?

Yes I agree with you. I think they are asking for the normal force. Thanks for the help.

Question: If someone is able to jump 2.0 m into the air a) How what speed must they leave the ground with?(ignore air resistance) b) If they are in contact with the ground for 0.25 sec and have a mass of 65kg, what force must they push off the ground with? Solution: a) Going from the...

If the question is what force do I need to push off the ground with, then aren't I looking for Fnormal and not net force? The force that I push off the ground with is equal/opposite to the force normal acting on me. So shouldn't I be solving FN - Fg = ma for FN?

Yeah, that's what I was thinking. Initially I was given the final velocity when jumping and the time in contact with the ground. Vf = vi + at That should be my net acceleration, because that is the actual acceleration needed to reach Vf.