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# Help, can anyone tell me my mistakes on this mechanics question? watch

1. A particle P passes through point A with velocity 2.8ms-1 and the constant acceleration 0.12ms-2. Three seconds later, a second particle Q passes through A with velocity 2.4ms-2 and constant acceleration 0.2ms-2.

Show that on the point meet, 2t2-50t-315=0. Where t is the time after P passes through A.

My following working:

Q:
S=?
U=2.4
V=?
A=0.2
T=t

then
P:
S=?
U=2.8
V=?
A=0.12
T=t+3

Insert into equation: S=UT+1/2AT2
=> Q is S=0.1t2+2.4t
and P is S=0.06t2+3.16t+8.94

As to have both equal
=> 0.1t2+2.4t=0.06t2+3.16t+8.94
=> 2t2-19t-447=0

Which meant that I must be wrong somewhere, but I can't seem to find the mistake.
2. Edit: You made a calculation error for P, the value independent of t (8.94) is wrong.
3. By on point meet do you mean when the two particles meet or what?
4. The time for P is just t, meaning Q is t-3
5. (Original post by FailingMath)
The time for P is just t, meaning Q is t-3
It doesn’t matter if you use t+3 and t or if you use t and t-3, as long as the time for P is 3 more than the time for Q.

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