Frictionless pulley- incline


by physics1234
Tags: frictionless, incline, pulley
physics1234
physics1234 is offline
#1
Sep25-06, 07:44 PM
P: 21
Two packing crates of masses m1 = 10.0 kg and m2 = 7.00 kg are connected by a light string that passes over a frictionless pulley. The 7.00 kg crate lies on a smooth incline of angle 43.0. Find the acceleration of the 7.00 kg crate up the incline. Find the tension in the string.

I found the acceleration (correctly) to be 3.0126 but I can't seem to get the tension part of the question. I tried the formula T=(m2)(g)(sinTHETA)+(m2)(a) using 7(3.0126)sin43+7(3.0126) and 10(3.0126)sin43+10(3.0126) but neither gave the correct answer.
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FunkyDwarf
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#2
Sep25-06, 07:47 PM
P: 479
This might be oversimplifying it a bit but shouldnt f=ma work?
physics1234
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#3
Sep25-06, 08:09 PM
P: 21
What would you use as the mass? 98 isn't the right answer.

RoyalewithCh33s3
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#4
Sep25-06, 08:46 PM
P: 15

Frictionless pulley- incline


Well, I'm just wondering on this one...but isnt the T of the string that is holding the block on the incline equal to the T of the string holding the hanging block?

So how would you figure out T on the hanging block?
FunkyDwarf
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#5
Sep25-06, 09:04 PM
P: 479
well no because theyre moving theyre not in equilibrium, i assume?

just write out how you got the accel so we can see how ur goin about this as i agree with ur workin for T so maybe accel is wrong? ( i know you said you got it right but just check)
RoyalewithCh33s3
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#6
Sep25-06, 09:12 PM
P: 15
Wouldn't they be moving in equilibrium? The string is not growing shrining, they are just shifting arent they?
physics1234
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#7
Sep26-06, 02:07 PM
P: 21
I got the acceleration by a= (m2-m1sinTHETA/m1+m2)g so it was (10-7sin43/17)(9.8) = 3.0126

We can check to see if we got them right on the internet so that's definately the right answer, i just can't figure out the second part.
yesiames
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#8
Sep27-06, 11:02 PM
P: 1
Quote Quote by physics1234
I got the acceleration by a= (m2-m1sinTHETA/m1+m2)g so it was (10-7sin43/17)(9.8) = 3.0126

We can check to see if we got them right on the internet so that's definately the right answer, i just can't figure out the second part.

try using the equation T= m1(g-a) = (10.0kg)[(9.80 - 3.0126) m/s^2] = 67.9N

i'm sure that's right cause i just did the same problem for hw.
good luck


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