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need help M2 projectiles question !!!!!

This is for Edexcel:

A particle p is projected with speed u ms^-1 at an angle of elevation B, where sin B = 0.6, from a point on horizontal ground. The particle moves freely under gravity. It hits the ground at a point which is 480 m from its point of projection.
Find
(a) the value of u
(b) the greatest height of P above the ground
(c) the time of flight

Reply 1

rayquaza17

What have you done so far? Post all working

Reply 2

tabmax22

Original post by rayquaza17

What have you done so far? Post all working

nothing. I don't even know where to start.

Reply 3

Jammy Duel

First thing you should do in ANY question: draw a diagram.

So, now I've quickly run through the question this is the rough route I took:
a) So, first I took the equations for the horizontal and the vertical displacements with time and considered them. The easiest one to pull the u figure from will be the horizontal displacement since we know what the distance is when it first hits the ground, we are given

\sin{B}

so we just need to find some term for t to pull out u.
To get u I then considered the vertical displacement, specifically when it is 0. To do this I factorised the equation and then took the contents of the bracket (obviously equated to 0) and rearranged it to make t the subject, I then substituted that back into the equation I got from the horizontal displacement and then u fell out quite nicely.
Note: while doing this is does look messy and as if it won't give a nice answer, but stick to it because it should.
b) When is the height greatest? when the vertical acceleration is 0, so then simply look at the relevant equation, plug in the necessary figures and t falls out quite nicely.
c) there are two ways to do this, the easy way and the way they probably want you to do it. The easy way is to assume your answer to b is correct and double it. The way they probably want you yo do it is just plugging the correct figures into the correct equations and then pull out the correct answer (there are several equations you can use and I touched I think 3 excluding the easy way).