mfb said:
I don't think it needs an explanation beyond that.
I'm curious? :P
Well, one of the answers is wrong, so I asked how you got them.
Thing is, this was a question on a paper we completed a while back, and I'm going back working out what went wrong.
"GPE would increase" was marked correct.
"Max velocity would increase" was marked incorrect. I figured that an increased mass would pull up the whole equation. And it would, but I forgot that the equation was for Ek and v is only a variable in that. So it would stay the same? Either that or my teacher is wrong.
haruspex said:
If you include the units all through that calculation you might spot a problem with that.
You divide J/s by seconds, so the result has units J/s2, which is not a useful quantity (and it certainly does not have J as unit).
If I give you 5 apples per second, and do that over 60 seconds, how many apples do you get?
300 apples! :D Yeah, that was clumsy. Thanks. So 11000 x 60 = 660000 J.
Don't forget the cart. No, you cannot just change the units. Think what you did for (a), the potential energy at the top of the hill. You can do the same thing with persons in the cart, and compare it to the energy available (which you still have to calculate in the right way).
Right, 750 + 70P kg < something.
So 660000 J is needed to operate the motor in total. Not sure how to proceed. I know GPE = mgh is going to come into this but I'd be fumbling in the dark. The energy available?
EDIT: Okay, conservation of energy. That 660000 goes somewhere, into GPE.
660000 = m x 9.8 x 40.
...
m = 1684 kg. There's my something.
750 + 70P < 1684
70P < 934
P < 13.3
13 people?
haruspex said:
Whether or not you can provide your reasoning as part of your official answer, you need to have a reason.
How will friction mean that more mass leads to a lower velocity?
The other significant loss of energy will be through drag. How will mass affect velocity when that is considered?
I'd guess that increased mass would decrease velocity, but that was marked incorrect. With respect to maximum velocity, anyway.
I'd also guess that Newton's third law comes into this, but doesn't more mass mean more force, and that added force would at least equal the added friction?