Newton's 3rd law

[stephenuk26]

Hello,

I just got asked this question in an online exam and I selected answer C. But the answer apparently is D....how?

Surely the mass of the walls is completely irrelevant as it's not adding a force to either skater (There's no attachment to the walls), if the skaters had rucksacks on with different mass' then I would not select answer C. Totally confused by this one... 

[Genady]

Looks like 55 kg and 110 kg are masses of the skaters rather than of the walls. Look at them, one is thin, and the other is not.

[Ghideon]

5 minutes ago, stephenuk26 said:

the mass of the walls

The masses A and B are incorrectly placed in picture, A and B should be above skaters instead if f above the walls?

 

edit: x-post with @Genady; good explanation.

Edited January 12, 2023 by Ghideon
Xpost

[Tutoroot]

True

[studiot]

17 hours ago, stephenuk26 said:

Hello,

I just got asked this question in an online exam and I selected answer C. But the answer apparently is D....how?

Surely the mass of the walls is completely irrelevant as it's not adding a force to either skater (There's no attachment to the walls), if the skaters had rucksacks on with different mass' then I would not select answer C. Totally confused by this one... 

I agree with Genady and Ghideon.

In fact if you read the text very carefully the text refers to skate A and Skater B.
The walls are referred to in the plural and not distinguished.

However you are correct in realising that the mass of the walls is irrelevant.
So take heart this was a very poorly drafted question.

I would be interested to learn where it came from please ?