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svirdi
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Block of mass 4kg rests on a smooth plane inclined at 20 deg to horizontal. It is connected by a light, inextensible string passing over a smooth pulley at the top of the slop at a 3kg particle hanging freely. Find the acceleration of the system and the tension in the string.

Ok so I started with:

F=ma

a=f(total)
M(total)

3*9.8 + 4*9.8sin20 = a
3+4

am I on the right track of how to get the acceleration?
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davros
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(Original post by svirdi)
Block of mass 4kg rests on a smooth plane inclined at 20 deg to horizontal. It is connected by a light, inextensible string passing over a smooth pulley at the top of the slop at a 3kg particle hanging freely. Find the acceleration of the system and the tension in the string.

Ok so I started with:

F=ma

a=f(total)
M(total)

3*9.8 + 4*9.8sin20 = a
3+4

am I on the right track of how to get the acceleration?
Where's the tension gone from your equations?

You basically want
motion of block: weight acting down the slope against tension pulling up, giving mass x acceleration for the block

and motion of particle: weight downwards acting against tension upwards, resultant gives mass x acceleration.for particle.

Since everything is smooth and the string is inextensible the tensions and accelerations are the same in each case.
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svirdi
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(Original post by davros)
Where's the tension gone from your equations?

You basically want
motion of block: weight acting down the slope against tension pulling up, giving mass x acceleration for the block

and motion of particle: weight downwards acting against tension upwards, resultant gives mass x acceleration.for particle.

Since everything is smooth and the string is inextensible the tensions and accelerations are the same in each case.
ahh

so you mean

T-Mg sin20=ma

T-Mg= -ma
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davros
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(Original post by svirdi)
ahh

so you mean

T-Mg sin20=ma

T-Mg= -ma
I'm not sure why you're mixing up M's and m's here.

The mass in the first equation should be the mass of the block on both sides; the mass in the 2nd equation should be the mass of the particle on both sides. Also it's simpler to write the 2nd one as mg - T = ma since the net movement is downwards, although it doesn't affect the arithmetic.
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svirdi
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(Original post by davros)
I'm not sure why you're mixing up M's and m's here.

The mass in the first equation should be the mass of the block on both sides; the mass in the 2nd equation should be the mass of the particle on both sides. Also it's simpler to write the 2nd one as mg - T = ma since the net movement is downwards, although it doesn't affect the arithmetic.
Ok thanx got it right
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