Help with mechanics question (1 Viewer)

[asiangamer01]

Hi everyone, came across this question as a past HSC question and I got stuck on part b) of it. Can someone please help me? It just doesn't seem to be working for me.

Thank you so much

 

[kawaiipotato]

Have you tried integratong both sides of part i and letting v = 0 for maximum height x?

 

[asiangamer01]

yeah i have. I get (1/2)(v^2) = 10r^2/(r+x) + c, then the conditions i used to find c are x=r, and v=400

 

[braintic]

Hi everyone, came across this question as a past HSC question and I got stuck on part b) of it. Can someone please help me? It just doesn't seem to be working for me.

Thank you so much View attachment 32328

Have you subtracted the earth's radius from the final x value?

Edit: Oops - read the question wrongly.

 

[asiangamer01]

yep and i end up getting an answer of like 30000, instead of the require 8000 something

 

[braintic]

You'll have to post your solution.

 

[braintic]

Actually I've found your problem.

The question says x is the distance above the earth's surface, not the centre of the earth.
So the initial conditions are x=0, v=400.

 

[InteGrand]

 

[asiangamer01]

thank you, now i got the answer