# active physics

from the question we just did, how much force is neede to stop in 20 seconds!

OK. think it through. If it's going at 10 m/s, and then it stops, what is it's change in velocity?

is it 10

Yes, now it takes 20 seconds, so what is its acceleration (actually deceleration)?

can u rephrase that

YOu remember your formula for accelertion that you stated before?
Well, you know the change in velocity, and you know the time...so the acceleration is...? (Deceleration is just the same thing as acceleration...it's slowing down instead of speeding up)

YOu remember your formula for accelertion that you stated before?
Well, you know the change in velocity, and you know the time...so the acceleration is...? (Deceleration is just the same thing as acceleration...it's slowing down instead of speeding up)

yes it was p=mv:p=500x10 p=5000

im talking about the problem which says what is the momentumof a 500kg object oving at 10 m/s

Right. Now, if I am understanding right, they are asking you what force is needed to stop this object in 20 seconds, right?

yes

OK, so, in order to get the force, you need to use the equation for force that BobPursely told you earlier. Do you remember the equation?

F=ma

Correct. So you need the acceleration to get the force. You remember your formula for acceleration?

is it a=change in velocity/time

Right. The change in velocity here...is it goes from a speed of 10 to a speed of 0. So it's change is...?

im stuck sorry

OK. It was going at a speed of 10...then it stops. (The force is stopping it). So the change in velocity is simply 10m/s (you take the final speed minus the initial speed to get the change in speed)...you don't have to worry about the negative sign here. So the change in velocity is 10. Does this make sense?

ohhh ok i get it that made more sence

So, the change in velocity is 10, and it takes 20 seconds to make that change, so the acceleration is?

is 30 im not sure

It is change in velocity/time. That means change in velocity DIVIDED by the time. 10/20 is 10 divided by 20, which is 0.5

ohh i forgot to divide

OK. Now that you know the acceleration, you go back to your force equation, and plug them in! (you know the mass, m of the object, and you know the acceleration, so you can get the force!)

is it 500x0.5

Bravo!!!!

so its 250.0

Exactly right. You did it!!

its cuz i barely started this source is it ok if i ask u snother question

OK, I understand.
I will be signing off, but feel free to post your next question, and I'm sure someone else can help you.

ok thx 4 da help

this is awesome!

yeah!!!

one more time!

hey!

m

thanks!

accounting!

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