Cambridge ENGAA physics questions

14 is asking about the coupling supporting the pulley.

if you ignore the acceleration and look at it as a static problem first, you can see that there's 50N tension in the left rope and 50N tension in the right rope... so the coupling has to take 100N before you even start increasing the tension by accelerating the mass.

dunno if you're misreading the question or just not familiar with thinking about pulley systems tbh.

Hi guys i posted my maths related questions in the maths forum, these are my physics ones. If anyone could help me out it would be much appreciated.

https://www.undergraduate.study.cam.ac.uk/files/publications/engaa_s1_question_paper_2016.pdf

Question 14:

Worked out tension in rope as 54N. Unsure as to why the answer is double.

Actual Answer: H

Question 52:

So i equated the change in momentum of the spacecraft and the momentum of the fuel. By rearranging and solving i got the mass of fuel as 4000/19 kg, which i approximated as 200kg, which is E.

However i also put 4000/19 into my calculator and the answer was 210kg which was F. I am not meant to be using calculators for this section and so i was wondering if i have gone wrong somewhere.

Actual Answer: E


Thanks in advance.

Just in case, you had not had an explanation for the answer for Q52.



Assume that the spacecraft is moving to the right relative to the earth, so the fuel is ejected to the left relative to the spacecraft.

As the fuel is ejected to the left at 1425 m/s relative to the spacecraft, the fuel is moving at (7425 – 1425 =) 6000 m/s to the right relative to the earth.

m_i is the mass of spacecraft

Δm is the mass of fuel ejected

v_i is the initial velocity of the spacecraft relative to earth (+7425 m/s)

v_f is the final velocity of the spacecraft relative to earth (+7500 m/s)

u_f is the final velocity of the spacecraft relative to earth (+6000 m/s)

Initial linear momentum = m_i v_i

Final linear momentum = (m_i – Δm) v_f + Δm u_f

m_i v_i = (m_i – Δm) v_f + Δm u_f

Δm v_f – Δm u_f = m_i v_f – m_i v_i

Δm = 200 kg

You can also use the relative change in the speed of the spacecraft and the relative speed of fuel ejected to solve the problem in an elegant way.

I did the change in momentum of the rocket equals the change in momentum of the fuel and solve for the mass of the fuel, which gave me the correct answer.

how do you do question 51 on the paper?

Integrate with respect to y to get the area enclosed by the curve and y axis.

Remember to make x=0 to find ur limits for the integration.

Thanks a lot- I think I got it now
do you think you could also help with 54?

Sorry i dont have much time to explain

Haha I did that paper two but couldn't finish the whole thing within the time limit so got about 73% but I continued doing it and ended up getting all of them correct according to the answer key- yea we got the same sort of working for the last Q

For the section two i got 15/24 in timed conditions, completely ballsed up section 1 tho, ran out of time.

So tomorrow im gonna goas fast as Usain