Solving a Problem: What Went Wrong & Velocity for Both Masses

Mohmmad Maaitah · May 6, 2023

This is the problem:

Printed exam question 19 with a pulley diagram: m2 = 2 kg on a frictionless horizontal surface connected over a pulley to hanging m1 = 6 kg; options a) 2.5, b) 10, c) 0, d) 7.4, e) 3, with d) circled.

And this the answer provided by the examiner:

Handwritten solution to a pulley problem with two masses: m1 on a hanging side and m2 on a horizontal surface, with equations T = 6a, mg - T = ma, 8a = 19.6, a = 2.45 m/s^2 and vf = 7.35 m/s; beside it a free-body diagram showing N, T and m2g on m2 and T and m1g on m1, with a pulley at the edge of the table.

And this is my own answer:

Handwritten physics working on lined paper: force equations for two connected masses, m1 = 6 kg hanging and m2 = 2 kg on a table, leading to a = 7.35 m/s^2 down for m1 and v2 = 22.05 with a question about whether the speed is the same for both masses.

So what did I get wrong???
Also I want to know if the Velocity is the same for both masses.

Doc Al · May 6, 2023

Mohmmad Maaitah said:

So what did I get wrong???

The diagram shows m_1 as the hanging mass, but the given solution switches that. Your work is fine.

Mohmmad Maaitah said:

Also I want to know if the Velocity is the same for both masses.

Sure---they are connected. (The speeds are the same, but they move in different directions, of course.)

Mohmmad Maaitah · May 6, 2023

Doc Al said:

The diagram shows m_1 as the hanging mass, but the given solution switches that. Your work is fine.

Sure---they are connected. (The speeds are the same, but they move in different directions, of course.)

Oh lord, he switched the masses :doh:

Solving a Problem: What Went Wrong & Velocity for Both Masses

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