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Mechanics 1 help

How do you work out initial velocity from a time-velocity graph when you are just given the average speed for the journey (37.5 m/s) and the deceleration between point 'T' and '2T', which is 2.5ms^-1. From the start to point T they are not not moving then decelerates. I have worked out that the distance travelled is 75t, which I'm not sure about. Any help would be greatly appreciated.
(edited 12 years ago)
Original post by tx639
How do you work out initial velocity from a time-velocity graph when you are just given the average speed for the journey (37.5 m/s) and the deceleration between point 'T' and '2T', which is 2.5ms^-1. From the start to point T they are not not moving then decelerates. I have worked out that the distance travelled is 75t, which I'm not sure about. Any help would be greatly appreciated.


Can you supply the question as worded in the book/whatever.
Reply 2
Avatar for tx639
tx639
OP
2
The question is 'Given that the average speed for the whole journey is 37.5m/s and that the deceleration between T and 2T is 2.5 m/s^2. find the value of V and T. It is accompanied by a graph that shows constant speed at velocity V until T where it decelates to 0.
Original post by tx639
The question is 'Given that the average speed for the whole journey is 37.5m/s and that the deceleration between T and 2T is 2.5 m/s^2. find the value of V and T. It is accompanied by a graph that shows constant speed at velocity V until T where it decelates to 0.


That makes more sense.

OK: You know average speed = "total distance" divided by "total time".

You're told the average speed.

You can get total distance in terms of V and T, from the area under the graph.

You know total time in terms of T.

So, plug those into your equation and you should be able to work out V (If not, post your working.).

See if you can finish it from there.
Reply 4
Avatar for tx639
tx639
OP
2
Thanks for your help! I managed to work it out :smile:
please send the working of the question , I have tried everything but nothing is working
(edited 4 years ago)
Original post by dylangoneso
please send the working of the question , I have tried everything but nothing is working


Thread is 8 years old, and OP hasn't logged on in over 6 years, so they've unlilkely to be of assistance. Also fully worked solutions are against forum rules. I suggest you start a new thread and post you're working as you say you've tried everything! You might find it helpful to read the maths forum guidelines - sticky thread at top of forum - as to what is expected in asking questions on here.
Reply 7
Avatar for BVERRIS
BVERRIS
1
(1/2(t 2t) * v) / 2t
= (1/2 * 3tv) / 2t

1/2 * tv = 37.5
tv = 75
v = 75/t
(edited 4 years ago)

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