Why body A has greater acceleration?

[Iamconfused123]

Homework Statement

question is which body A has greater acceleration?

Relevant Equations

F=ma

Apparently body A has greater acceleration and I don't get why. Can someone please explain.

It's stated to take g=10/s^2.
Both bodies have same mass.
Nothing about rope elasticity is added, and nothing about the pulley. So I assumed they are both massless, and no friction between them.
Also, the table surface is frictionless.
Thank you

 

[PeroK]

The pulley and string may be massless, but the 1 kg mass is definitely not massless!

 

[Iamconfused123]

yeah but, 1kg×10m/s^2=10N so both forces are the same, masses the same, thus accelerations are the same

 

[Orodruin]

yeah but, 1kg×10m/s^2=10N so both forces are the same, masses the same, thus accelerations are the same

No, they are not. If the tension in the string were 10 N then the net force on the 1 kg mass would be zero and it would not accelerate.

 

[PeroK]

yeah but, 1kg×10m/s^2=10N so both forces are the same, masses the same, thus accelerations are the same

Yeah but, the 1 kg mass is not massless.

 

[Iamconfused123]

No, they are not. If the tension in the string were 10 N then the net force on the 1 kg mass would be zero and it would not accelerate.

But the bodies(A and B) are not connected, if that is what you are saying.

 

[PeroK]

But the bodies(A and B) are not connected, if that is what you are saying.

The 1kg mass is connected to B.

 

[Iamconfused123]

The 1kg mass is connected to B.

Okay, but why does that matter? 1kg is falling with 10N pulling B with 10 N, same force as the hand is pulling A

 

[PeroK]

Okay, but why does that matter?

It;s fundamental.

1kg is falling with 10N

What does that mean?

pulling B with 10 N, same force as the hand is pulling A

Is it? What about Newton's third law? If the 1 kg mass pulls B with a force of 10N, then B pulls the 1kg mass with an opposite force of 10N, and the 1kg won't move, as it has a zero net force acting on it.

 

[erobz]

May I suggest drawing free body diagrams of each mass ( A,B, and 1kg) for us to examine together?

 

[Iamconfused123]

ohh. I figured. How stupid am I

 

[Iamconfused123]

Thanks everyone.

 

[Iamconfused123]

May I suggest drawing free body diagrams of each mass ( A,B, and 1kg) for us to examine together?

Like, I never draw those. And the best thing is that I have solved whole bunch of problems with like these, but they were like, calculate acceleration. I did take a brake from physics for 2 weeks or so, but still, like I knew how to do these problems. Is it normal for people to forget that fast?

 

[erobz]

ohh. I figured. How stupid am I

It's not that big a deal. It's tricky like that on purpose. Thats why its important to draw a FBD, because it becomes apparent when to "see" the forces.