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# SUVAT question query? Watch

1. 14. A particle moving in a straight line with constant acceleration takes 3s and 5sto cover two successive distances of 1m. Find the acceleration

I got these 2 formulas

1=3u+4.5a
2=8u+32a

Why cannot i use this method to find a?

1=3u+4.5a *8
2=8u+32a *3

I've tried doing it this way but get the wrong answer and instead have to work it out by substitution and am wondering why this method doesnt work and when to know when to use which method
2. (Original post by ErniePicks)
14. A particle moving in a straight line with constant acceleration takes 3s and 5sto cover two successive distances of 1m. Find the acceleration

I got these 2 formulas

1=3u+4.5a
2=8u+32a

Why cannot i use this method to find a?

1=3u+4.5a *8
2=8u+32a *3

I've tried doing it this way but get the wrong answer and instead have to work it out by substitution and am wondering why this method doesnt work and when to know when to use which method
You need to multiply both sides by 8 and 3.
3. (Original post by Zacken)
You need to multiply both sides by 8 and 3.
sorry i have another suvat question

for this question

A train stops at two stations P and Q which are 2km apart. It acceleratesuniformly from P at 1ms-2 for 15s and maintains a constant speed for a timebefore deceleration uniformly to rest at Q. If the deceleration is 0.5ms-2 findthe time for which the train is travelling at a constant speed

I calculated that during the first acceleration stage the V=15 m/s so for the constant speed phase i got

U=15
V=15
A=0
T=?

Why cannot i use v=u+at to find t? is it because 0 doesnt count as constant acceleration? (i mean it's constantly zero..)
4. (Original post by ErniePicks)

U=15
V=15
A=0
T=?

Why cannot i use v=u+at to find t? is it because 0 doesnt count as constant acceleration? (i mean it's constantly zero..)

You can use it, 0 is constant acceleration. It's just that your equation is useless.

It's like asking "why can't I use 1 + 1 = 2 to find t?"; 1 + 1 = 2 is a true equation but it's useless to the specific scenario at hand.
5. (Original post by ErniePicks)

Why cannot i use v=u+at to find t? is it because 0 doesnt count as constant acceleration? (i mean it's constantly zero..)
if a=o then v=u+at is just v=u since it is the same as v=u+0t and anything times zero is still zero

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