IAL Physics Unit 5 - 15 Jan 2021

I know everyone is nervous for the results releasing today and so I am! However, if anyone will take the exam this Friday, feel free to discuss here! Good luck for all!

Can somebody tells me the answers of the following questions?
1 wavelength shift by using Doppler formula
2 impulse used to change frequency from 60Hz to 240Hz
3 reason for the space station burn itself
4 reason for the acceleration of two collided galaxies

I was also confused about these questions but for 4, I wrote that when they towards each other, the gravitational force is increased and hence, the acceleration is increased

It is so strange that the Doppler formula question involves two pairs of wavelength.

It is so strange that the Doppler formula question involves two pairs of wavelength.

That’s why I calculate for both and found the speed are almost the same

I give the two significant figure answer as the two values are coincide, but three significant figure answers differ a little bit.