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Projectiles A2 Mechanics (please help)

Hello, can someone please check my answers to the below question
Thank you very much.


A particle is projected horizontally at 2.5 m s1 from a height of 400 m. Assume that there is no air resistance and take g= 10 m s2.

a) Find the particle's height after 8 seconds.

b) At what time is the vertical component of the particle's velocity equal to 65 m s1?

My solutions

(a) s=Ut + 1/2 at^2
4.9× 64
313.6
400-313.6
=86.4 m

(b) v=u+at
65= 9.8t
t= 6.6 s
Reply 1
This seems right to me if we’re using 9.8 as g/a. Your working all seems right too.
Note: I'm going to be a bit harsh, because no one at 8am or anytime of day really want to decipher steps and formulas and stuff without explanations.

I think the idea is there. Numerically the answer looked about right.
However do note that you were told to use g=10, not 9.81.

You probably want to write down some words to describe what you're trying to do.
For instance, I think you are trying to do two things in (a). Well, what are those two things?
Note the lack of equal signs. A number 313.6 floating around in the middle of your work means nothing.

Also, pay attention to signs.
For instance, you are saying acceleration (due to gravity) is positive. Why positive?
Not wrong per say in this instance, but when the system gets complicated, you might get confused.
(edited 7 months ago)
Reply 3
Thank you very much for you valuable advice and time. 👍
Reply 4
Original post by tonyiptony
Note: I'm going to be a bit harsh, because no one at 8am or anytime of day really want to decipher steps and formulas and stuff without explanations.

I think the idea is there. Numerically the answer looked about right.
However do note that you were told to use g=10, not 9.81.

You probably want to write down some words to describe what you're trying to do.
For instance, I think you are trying to do two things in (a). Well, what are those two things?
Note the lack of equal signs. A number 313.6 floating around in the middle of your work means nothing.

Also, pay attention to signs.
For instance, you are saying acceleration (due to gravity) is positive. Why positive?
Not wrong per say in this instance, but when the system gets complicated, you might get confused.

Thank you very much for you valuable advice and time. 👍

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