Physics problem!

[TheDave]

maybe it means mps+0.25m=mps

[manker]

Does anybody know how to do this problem? I really dont know how to even start.

A block slides down an inclined plane 9m long that makes an angle of 38 degrees with the horizontal. The coefficient of sliding friction is 0.25 If the block starts from rest, find the time required for it to reach the foot of the plane

You'd need the weight of the block to determine this.

I'm looking at it and logically a housebrick will take longer to travel down the 9m slope than a bit of lego

Anyway, I think you'll need to use trigonometry too so look at the question in context with what else you're learning in school. I suspect the answers will be there if you look.

[TheDave]

what about greased brick vs sticky lego

[manker]

Greased brick

[ZaZu]

Guy hit me inna head with a greased brick once....once

[DawG_M]

There must be some way to do this w/o mass since he didnt give it to us.

[DarthInsinuate]

i don't think you need the mass because you can work out time from just acceleration and starting speed

edit: and distance

[TheDave]

i dont think we have acceleration

[DarthInsinuate]

acceleration due to gravity, argh i hate this thread, i did slopes and friction for my coursework i should know this, but i don't

[Barbarossa]

Heres some equations that may jog your memory:

distance = 1/2 * acceleration * time squared.

Therefore, time = square root of twice the distance divided by the acceleration. [t = SQRT(2d/a)]

So we need to find the acceleration, but all we've been given is the friction coefficient and the angle of incline. We haven't been given mass, so I must assume that it somehow cancels out in a minute.. (?)

Anyway, "Normal" Force = Mass * Acceleration Due to Gravity * Cosine(Angle of Incline)

Force of Friction = "Normal" Force * Friction Coefficient

Now the force of friction acts in the opposite way to the "Normal" force, so the net force = Normal Force - Force of Friction, which basically is the Normal Force times (1 minus the friction coefficient) ..

Therefore, the acceleration down the slope is Net Force / (Mass * Sine(Angle of Incline))

If we combine all this we get: A = M*G*Cos(S)(1-U)/M*sin(S), and so yes, M cancels out, so A=G*Cos(S)(1-U)/Sin(S)

G=Gravity=9.8
Cos(S)=Cos(38) = 0.7880107536
Sin(S)=Sin(38) = 0.6156614753
U=Friction Coefficient=0.25

Therefore A=Acceleration down the slope = 9.407570997

Therefore, T= SQRT(2d/A)

A=Acceleration=9.407570997
D=Distance=9

T=1.383239876 SECONDS.

Fuck me, that was quite hard, it's over a decade since last did an exam..

Don't come crying to me if it's wrong. I'd put money on it..