Archive for the ‘Collisions’ Category

January 13, 2014 · by physics · Acceleration, Collisions, Momentum

Popeye, of mass 70kg has just downed a can of spinach. He accelerates quickly and stops Bluto, of mass 700kg (Bluto is very dense), who is charging in at 10 m/s. What was Popeye’s speed?

a. 10 m/s
b. 31 m/s
c. 50 m/s
d. 100 m/s

Raw Transcript

Hello this is Tom from every step physics dot com going to an actual physics problem from a test final
and I’m gonna do number nine here on this sheet, I’ll show you the sheet let’s do it I’m going to scroll down to collisions and this next one in the problem it says that he stops Bluto so that word is a key one whether it’s a momentum or collision problem. Now this is a special collision problem because when it says stop that means that both of the well after they hit they stick together and stop so that means that
the final velocities are 0 for both of them so it’s a special momentum problem maybe a trick problem
a lot of trick problems in physics as if physics wasn’t hard enough and we’re gonna find what are we gonna find we’re gonna find Popeyes initial…um velocity so we’re going to choose Vi1…we’re going to enter the mass Alpha is 0:00 kilograms, you have to press alpha to enter anything into my entry lines here and Bluto is 700 kilograms initial velocity of Bluto is 10…Bluto is 10 meters per second oops, press Alpha first and he’s going to the left, Popeyes going to the right so we choose -x axes and you can see if it’s correct, which it is, you can change it if you you wanted and so the momentum of Pluto is mass times velocity which is his mass is 700 plus that which is minus 7000 kilograms meters meters per second and since one of the laws of physics is that p1 plus p2 equals zero, so we enter that in the equation and then we solve for p1 with becomes a positive 7,000 that’s what the momentum of Popeye is and so we do the calculations here we come up with 100 meters per second for Popeye which is on the test you just circle that one and get a hundred percent on problems like that, pretty neat huh? every step physics dot com.

January 6, 2014 · by physics · Collisions, Physics Test Questions

A 20-kg object sitting at rest is struck elastically in a head-on collision with a 10-kg object initially moving at +3.0 m/s. Find the final velocity of the 20-kg object after the collision.

a. -1.0 m/s
b. -2.0 m/s
c. +1.5 m/s
d. +2.0 m/s

Raw Video Transcript

Okay this is Tom from every step physics dot com we’re gonna work an actual physics problem here problem number 8 on my sheet which I’ll shall show you and let’s do it get to my menu you know it’s a collision or momentum problem..ah because the words and so you know scroll down here to collision
and this decide which from other words in the problem with what they’re talking about in this case number eight they’re talking about a head-on collision so we’re gonna choose 2 which is collides and we’re going to do head on which is 7 I show you the formula for the final velocity of mass 1 and mass 2 final velocity this is the actual formula you can see CR here whic is the coefficient of restitution that’s the bounce ability of a substance and sometimes they give you that to enter into the problem or not and if they do then you’re in good shape here but they find this out by experimentation and the lists of substances about what they’re coefficient of restitution is for instance a super ball which is the most bouncy thing on earth is .78 coefficient of restitution doesn’t come up to one because if it came up to one that would mean that if you drop it from a hundred feet it would bounce right back up in your hand which gravity won’t let it do it so there is no possibility of one clay as an example the coefficient of restitution of zero and that defines whether it’s a perfect elastic collision if it has a coefficient of one or a perfectly inelastic collision which is sticking to mass is sticking and not bouncing off at all so let’s continue here um here’s a note here, if an object is at rest that’s the m2 mass to enter here so we have to press alpha first gonna press alpha and put in the mass that’s not at rest which is 10 you choose kilograms that’s what it says the second mass alpha twenty also kilograms initial velocity is coming at it at what does it say 3 meters per second we choose number three here and it’s going in the easterly direction or the plus X axis direction choose that and we have the initial velocity of the the mass 2 which is at rest if its at rest we enter 0 Alpha 0 and coefficient of restitution if it’s not given just enter one alpha 1 I show you what you’ve entered you can change it if you want looks pretty good to me were going to say okay and I give you both final velocities of both because they’re both gonna bounce off somewhat go somewhere and so the velocity final velocity mass 1 was minus point one notices its going off to the left there with the minus sign after they hit and here’s the final velocity mass 2 and 2 is positive so it’s going off to the right two meters per second so that’s the calculations notice on the test they do have plus 2 is meters per second and so you circle that one and get a hundred percent on it pretty neat huh..every step physics dot com and because you know its a collision problem our momentum problem you’re going to scroll down to a collision if you didn’t know it was that

October 20, 2013 · by physics · Collisions, Velocity in Physics

 Raw Transcript

This is a video from demonstrating how my programs work and the TI-89 titanium calculator and other calculators and the TI system for physics and calculus problems. For my program you have to press second alpha to put the letters physics in here and then press L for the open and close parentheses press ENTER and you get into my menu. We’re talking about a collision of two balls we’re gonna get on here too scrawled on alphabetical to you collision and we were given two masses into initial velocities which is number four here so we’re going to scroll down we could press the number before or scrolled one and a silastic site areas bounced off they bounce off and here’s the initial formally
rate this right on your paper right away already you get three points partial credit for the problem which is
always the way testers court in physics and calculus am going to enter our first mass and the
first mass would be alpha point 6 for 0 kilograms by the way have to after Press alpha before you enter anything in them I am felines my programs for calculus or physics and the as for the second mass metaphors alpha and point a to 0 kilograms initial velocity mass one would-be given for 3 point for meters per second in the plus axes close X axis direction East and the initial velocity for the second mass is elf 0 I will show you what you’ve entered see can change it if you want looks pretty good say it’s okay and you start writing is forming is down via for nichols’ the et cetera et cetera yeah the variables just like this don’t even think about the problem write it down and final velocity one ball is minus points 419 figure out the next 1 keep writing and your papers quite a long problem and the blasier the second masses 2.9 you per second and I some up losses here for you need every step physics that go to my site by my programs and pass physics.