Using the SUVAT equations

I know that suvat equations are for constnt acceleration only. I've just been trying to do a question from my text book and i've realised that 2 of the forces have different units, one is speed at 15ms-1 (-1 in small case) and the other being deceleration of 8ms-2 (-2 also being in small case). How am i supposed to make both of these units either ms-1 or ms-2, cause they can't be the same. Thanks (i hope it made sense)

Reply 1

yusufu

16

speed and acceleration are not forces.

Reply 2

insparato

15

This is because Speed and deceleration are different things.

Speed is a scalar quantity - Has ONLY magnitude

Deceleration is a vector quantity - Has both magnitude and direction.

Using dimension analysis (is that the correct term?) to find out units of things.

Deceleration = Final velocity - initial velocity / Time

Velocity is measured in ms-1

Deceleration = ms^-1/ s^1

using indices Deceleration - ms^-2

Speed = Distance/ Time

Speed = m/s = ms^-1

Yeah and speed and deceleration arent forces

Reply 3

insparato

15

Acceleration is always in ms^2 and speed or velocity is in ms^-1.
Due to the original equation it comes from.

S = ut + 1/2at^2 -- Displacement is in metres
V^2 = u^2 + 2as -- Final velocity is in ms^-1 (metres per second)
S = u+v/2 x t --- Displacement in metres again
v = u + at -- Final velocity is in ms^-1

Its just a unit for measuring different quantities.

You can have 12 of anything but the unit defines what magnitude tells us.

A number is just a magnitude .

12 elephants
12 metres
12 seconds
12 ms^-1 -- 12 metres per second
12 ms^-2 -- 12 metres per secound per second (bit confusing dont worry about it)

ms^-2 tells us its a deceleration or acceleration 12 ms^-1 tells us its the speed or velocity of something.

Reply 4

gyrase

3

Becky68M

so the -1 and -2 thing doesn't matter if they aren't the same?

If -1, then it is velocity, if -2, then it is acceleration.

Reply 5

ianbates1

1

Try thinking of it like this,Velocity is -1 an object might be moving at 4ms-1 so this is a constant non changing speed if you will it will go 4meters in 1 second and then another 4m in the next second and so on.Where as acceleration is -2 so at 4ms-2 it will increase it's velocity 4m in the first second 8m in the second 12m in the next it is gaining 4ms every secondIan

Reply 6

spotify95

18

Original post by ianbates1

Try thinking of it like this,Velocity is -1 an object might be moving at 4ms-1 so this is a constant non changing speed if you will it will go 4meters in 1 second and then another 4m in the next second and so on.Where as acceleration is -2 so at 4ms-2 it will increase it's velocity 4m in the first second 8m in the second 12m in the next it is gaining 4ms every secondIan

Hi, just to let you know, you're probably better off creating a new thread rather than replying to one that is over a decade old. :yep:

Using the SUVAT equations

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