Question about finding midpoint

Sha.xo527

Screenshots attached

Reply 1

Sha.xo527

Original post by Sha.xo527

Screenshots attached

This is the question context:
Screenshot 2024-03-29 150510.png

This is the question:
Screenshot 2024-03-29 150550.png

This is the mark scheme:
Screenshot 2024-03-29 150647.png

My question is, how is yi 61.221? I thought yi would be 65 (40 + 50/2 = 65), so why 61.221?

(edited 4 weeks ago)

Reply 2

mqb2766

Original post by Sha.xo527

This is the question context:
Screenshot 2024-03-29 150510.png

This is the question:
Screenshot 2024-03-29 150550.png

This is the mark scheme:
Screenshot 2024-03-29 150647.png

My question is, how if yi 61.221? I thought yi would be 65 (40 + 50/2 = 65), so why 61.221?

It would only be 50/2 if the second shape was a rectangle of height 50. Its a semicircle. Your formula sheet should have the 4r/3pi formula?

Reply 3

Sha.xo527

Original post by mqb2766

It would only be 50/2 if the second shape was a rectangle of height 50. Its a semicircle. Your formula sheet should have the 4r/3pi formula?

I have the formula sheet, but how does the shape being a semi circle mean you don’t divide 50 by 2? Can you talk me through how 61. 221 was gotten please?

Reply 4

mqb2766

Original post by Sha.xo527

I have the formula sheet, but how does the shape being a semi circle mean you don’t divide 50 by 2? Can you talk me through how 61. 221 was gotten please?

Its the com of a semicircle. Theres more the mass towards the bottom so the com cant be in the middle? It should be in your textbook or a quick google something like
https://www.youtube.com/watch?v=IS6SKLVT3Sk

Reply 5

Sha.xo527