Physics Lesson: Pulley on a Ramp Problem (Advanced) for high school

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[xxxEnChantedxxx]

Why will acceleration (a) end up being zero? Do we conclude that it's stationary because friction > acceleration?

Thanks so much!

[PhysicsEH]

@xxxEnChantedxxx The friction formula calculates the maximum friction available. If you pull an object with 4N and you calculate the friction as 5N then you actualy only get 4N of friction since that is all that is required and the object will stay at rest. In this example the maximum friction was more than required so there was more than enough to keep it at rest so the accel = zero. That is, the max friction is larger than the total force pulling it to move. i hope this helps.

[mytkt93]

THANK YOU = ). It helps me a lot.

I have another question, why the system will not start when the acceleration calculated is negative? Negative acceleration means the 5kg object remains stationary or moves down the hill? My problem is that I don't understand what is the negative accel stands for. Thank You

[PhysicsEH]

@mytkt93 When you start this type of question you need to guess which way it will accel. If you guess right, the accel is positive. If you guess wrong, it ends up negative. If it ends up negative you can't just say the accel is the other way because the calculation is wrong. You need to start the question again assuming it will accel the other way and the free body diagram will end up different (the Ff would be the other way) As a result the accel will be a different magnitude. Hope this helps.

[mytkt93]

if the acceleration of the object is negative, how can I explain the situation of the system in order to say that the system will not start.? Thank you. = )

[PhysicsEH]

@mytkt93 Hi. If the system does not start then the forces in the x-direction on each mass is balanced so on the 5kg the equation becomes Ft - Fgx - Ff = 0 and not "ma" since the acceleration is zero. You can now figure out Ft since you can find Fgx and Ff. The easier way is to look at the 3 kg object. The equation for this is Fg - Ft = 0 since the accel is zero, so Fa = Fg or 3*9.8. When the sytem does not move the question is much easier. I hope this helps.

[krazykrutz00]

you remind of that genius guy from "the hangover"!!

[matiarjafari]

@PhysicsEH so im confused as to what keeps the system staitionary rather than going down the ramp? in other words why doesn't the 5kg body on the incline slide down pulling the 3kg body?

[azharmohammed0]

BOO!!!! you suck lol

[Zeraan1337]

How can you just cancel the tension and put 3(9.8) in for it?

[PhysicsEH]

@ipodvidoe Thanks. glad to help.