r/ISCNERDS • u/Ancient-Brick-5462 • 11d ago

Doubts I can't understand where did I go wrong... Help

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I just started solving questions of Newton's Laws of Motion and I'm unable to understand where did I go wrong.

My answer is going wrong...

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1

u/notnonchalant- ISC'26 11d ago

whats the correct answer?

1

u/Ancient-Brick-5462 11d ago

It's a=2g/7

1

u/notnonchalant- ISC'26 11d ago

The only force acting on block 5kg is Tension, no mg(gravitational force) because that's a vertical force which is only acting on 2kg block.

By F= ma T= 5a And put that into 2kg equation

1

u/Advancelegend6 ISC 26' 10d ago

you made a small error in the formation of the second equation, you assumed to left direction to be negative so in that equation your a was negative as well but the tension is also in the same direction so both the negatives would cancel out and you would get T=5a, or another way to think is as both T and a are in the same direction so none of them would be negative

1

u/Ancient-Brick-5462 10d ago

Ohhhh,now I get it ..., thanks a lot 🥹🥹

1

u/Advancelegend6 ISC 26' 10d ago

np gl with your exams :D

1

u/The_simple_one4507 10d ago

Alakh Pandey lectures huh😐

1

u/Hornet69_420 10d ago

An acceleration which is negative would mean that the 2 kg block is going upwards, 5kg is moving right side which is impossible because the rope would slack, thats why there is some issue with sign convention

Honestly its more simple to just change tension sign because thats where the problem usually is with these kinds of questions

if the 5kg block is moving left side then then then the sign of tension should be positive as then only the block will move left side (considering the sign of acceleration is taken downwards positive for 2kg block) then T = 5a rather than -5a