Semester review: impulse, circular motion, momentum

[Zoe]

I've got a few questions on a "semester review" that I'm not understanding fully, and can't find the answers or explanations in my book. I'd be incredibly grateful if somebody could explain any or all of them to me!

For a lot of them, I have an idea of the answer but I'd like to know the reasoning behind it. Some is because I just haven't dealt with it for a while, and so might just need a refresher to be able to answer correctly.

Why does a baseball player follow through when he hits the ball? (I know this has something to do with impact/impulse, but I'm not quite sure.)

A ladybug on the inside of a spinning wheel will experience a force like gravity. (True/False question. I'm thinking true - I remember talking about spinning spaceships creating a gravity effect. How does this work?)

To increase rotational inertia, a tightrope walker carries a long stick. (True/False.)

If you squeeze a loaf of bread, its mass and density will increase. (True/False. I know density will increase, not sure about mass.)

A cannonball is fired at some angle and moves 10 meters horizontally in 1 second. How far will it move in the next second? (...no idea.)

A car is moving in a circle at a constant speed. What is the net force acting on it?

A car accelerates from rest to 20m/s in 10 seconds. It weighs 10,000 Newtons. What is the force on the car?

Essay Question:
Describe how Newton's three laws can be applied to a rubber ball that bounces off the wall of a no-gravity spaceship. Where is momentum conserved? (I can get through the law of inertia and action and reaction, but I'm not sure how force and acceleration applies to this. And again, I don't remember what momentum "being conserved" is. Sorry!)

Thank you so much for any help. :)

 

[plusaf]

Why does a baseball player follow through when he hits the ball? (I know this has something to do with impact/impulse, but I'm not quite sure.)

+af: what would happen if he stopped the bat at the instant of impact?


A ladybug on the inside of a spinning wheel will experience a force like gravity. (True/False question. I'm thinking true - I remember talking about spinning spaceships creating a gravity effect. How does this work?)

+af: did you ever take one of those rides in an amusement park where you stand against a metal cage with maybe a hundred other people, all facing inward, and the "wheel" starts to rotate, and when it's up to a good speed, you feel forced against the cage at your back, then they drop the platform away from your feet, and then they tilt the whole machine, and you don't fall out? what keeps you pressed against the inner wall of that ride? (clue?)



To increase rotational inertia, a tightrope walker carries a long stick. (True/False.)

+af: what does "rotational inertia" have to do with a tightrope walker? why would she want more rather than less? would a long stick be better than a short stick? why?


If you squeeze a loaf of bread, its mass and density will increase. (True/False. I know density will increase, not sure about mass.)

+af: why do you "know" density will increase? what's causing the density to increase (hint: you're squeezing the air out of the bread, and...). what could cause the mass of the loaf of bread to change? are you doing any of that to the loaf of bread? :)


A cannonball is fired at some angle and moves 10 meters horizontally in 1 second. How far will it move in the next second? (...no idea.)

+af: assuming there's no air resistance affecting the cannonball, are there any forces acting on it after it's fired that would change its HORIZONTAL speed? yes or no? if yes, what's the force? if there's no air resistance, what are all of the forces acting on the ball, and in what direction(s) do they act?


A car is moving in a circle at a constant speed. What is the net force acting on it?

+af: what kinds of information are needed to solve this problem? its speed? its mass? the diameter of the circle?


A car accelerates from rest to 20m/s in 10 seconds. It weighs 10,000 Newtons. What is the force on the car?

+af: there is a classic equation which relates force to mass and acceleration. Whom can you thank for it? c'mon, cough it up... :)


Essay Question:
Describe how Newton's three laws can be applied to a rubber ball that bounces off the wall of a no-gravity spaceship. Where is momentum conserved? (I can get through the law of inertia and action and reaction, but I'm not sure how force and acceleration applies to this. And again, I don't remember what momentum "being conserved" is. Sorry!)

+af: suggestion: start with the definitions of the laws, and then describe in words what's happening to the ball and to the wall as the ball hits the wall and after it bounces off the wall.


Thank you so much for any help. :)

i hope this helps.
just for calibration, what grade are you in?
thanks!
+af

 

[Zoe]

Thanks very much, that did helped a bunch! When you said "that classic equation that relates force to mass and acceleration," I was thinking "What?...oh DUH!" ;) Oh, and I'm in 10th grade.

Thanks again!

 

[plusaf]

Thanks very much, that did helped a bunch! When you said "that classic equation that relates force to mass and acceleration," I was thinking "What?...oh DUH!" ;) Oh, and I'm in 10th grade.
Thanks again!

A pleasure to help. i hope some of the other suggestions helped, too. I'm one of those obnoxious kinds of "teachers" who thinks that the best kind of learning happens when the student gets the "AHA!" on their own, after maybe some gentle nudging in the "right direction."

another hint which might help you is to get yourself familiar with as many of the basic physics equations as you can... then, when faced with a problem, see if you can list, from the description in the problem, which factors are provided... if, in that example, you're given mass and acceleration, even before they ask for the force, you might be thinking... M, A... M, A... ah! f=ma... and guess what they're asking for... f! practically done deal.

one other thing, that i think virtually nobody is going to tell a tenth-grader, is to take a look at yourself and how you learn things best. do you visualize a picture of a problem (or a solution) as you're working on it or learning the basic theory, or do you "talk yourself through it" with the little voice in your head describing the process in words.

the difference is called "visual" versus "auditory" learning and memory. if you tend to use one of the two "styles" more comfortably, focus on using that for learning the theory and creating the solution.

i'm very "visual". i can't solve a problem well if i can't picture what's happening in the problem, in my head. i learned my multiplication tables by memorizing what the answers "look like", and since i was about your age until now, i can still multiply from 1*1 to 9*12 in my head. i just "see the answer" without doing the math in my head, so to speak. same for addition.

if you can figure out a technique that helps, use it! it makes whatever you're learning more fun, too... wish i'd figured out something like that for social studies back then...