Physics 4.7.4a - Friction Practice Problems 1 - 2

[owaisoz]

why dont u have videos about work, mechanical energy, and its conservation, momentum and collisions ?

[derekowens]

@owaisoz I do, lots of them! I just don't post them all here. Students who enroll in a class get access to all of the videos for the class.

[sweetgirl94949]

wouldan answer of -40 be right also?

[TaraLynn218]

I appreciate everything youve done here, but the symbol for the coefficient of friction is pronounced mew, not moo

[nutella871]

Ahh thanks to this video, I just had a light-bulb moment. Much appreciated ;) You have lovely, legible handwriting and articulate explanations :D

[brjesusfreak]

How did he get the 9.8 m/s^2from? sorry, it is probably a noob question, lol.

[derekowens]

@brjesusfreak That's the acceleration due to gravity, in metric units.

[99miyah]

great. thanks!

[99miyah]

Can we say that the net force equals - f, because we determined that the positive direction is to the right, and the frictional force is opposing the car's motion?

[derekowens]

@99miyah Yes, that would be a very good way to set this problem up. You can define "to the right" as being the positive direction, and then the force of friction would be negative. That would be a pretty intuitive way to think about it.

[Itswalrus]

When converting km\h in meters can you just divide the number by 3.6? 90/3.6=25

[derekowens]

@Itswalrus Yes, that will convert from km/h to m/s. That's a helpful shortcut.

[UCSDMRod]

@Itswalrus where you getting the 3.6 from?

[Itswalrus]

@UCSDMRod That`s what my physics teacher told me

[UCSDMRod]

@Itswalrus but is 3.6 always going to work when converting km/h into m/s ? and if so where do the numbers come from like is it a law or something ahah

[Itswalrus]

@UCSDMRod I think it comes from 10^3=1000, and 1h=60, 3.6 or something like that. It should always work.

[mvayne80]

Thank you very much. I dont have the greatest physics prof in the world so much of what i learn is out of class. It would be a lot tougher if people like you didnt care to help us out with these type of videos.

[OoOIvaNOoQ]

I am confused about the forward force.

The forward force is not happening now?

But if i stand in front of that car, force will be exerted on me by that car?

[derekowens]

Yes, there will be a forward force on you, but right now we are concerned with the forces on the car, and only those forces. The forces on the car are the ones which determine the motion of the car.  In fact, if the car hits you, the force on the *car* will be backward, not forward!