[Mechanics] Questions using Suvat equations (motion equations)

username1393226

2

Completed

(edited 9 years ago)

Reply 1

Parallex

6

First of all, find u.

v = u + at[br]this becomes u = v-at[br]v = final velocity[br]u = initial velocity[br]a = acceleration[br]t = time[br]

then sub these values into

s = ut + \frac{1}{2}at^2

to find displacement

and well you've already worked out part b) from this working out.

You got the right answers so I don't really see a problem. :tongue:

(edited 9 years ago)

Reply 2

username1393226

OP

2

Original post by Parallex

I think your first problem is that you've got the wrong equation.

It's

s = ut + \frac{1}{2}at^2

where:

s

= displacement

u

= initial velocity

t

= time

a

= acceleration

I couldn't use that as I dont have the initial velocity ?

Reply 3

Parallex

6

Original post by T-GiuR

I couldn't use that as I dont have the initial velocity ?

yeah I realised that after I re-read it. Edited^

Reply 4

username1393226

OP

2

Original post by Parallex

yeah I realised that after I re-read it. Edited^

Thank you

Reply 5

Parallex

6

Original post by T-GiuR

Thank you

No problem, have fun. :smile:

Reply 6

lukejoshjames

7

For Part A, you've done the correct thing. The 16m/s is for final velocity, so that is it's velocity when it has stopped accelerating and is now at constant velocity. The velocity isn't constant while it is accelerating, however it is constant when it no longer accelerates.

For Part B, you have the correct equation, just sub the values into it after rearranging for initial velocity, u, which seems to be what you've done, except you've mixed 'v' up with 'u'.

EDIT: Nevermind, I see it's been answered :P

(edited 9 years ago)

Reply 7

User1443542

11

Original post by T-GiuR

First time doing mechanics and just wanted to see if what I was doing was correct please.

[I dont quite understand this as If a particle is accelerating than it's velocity can't be constant.]

Thanks

The required state to use the suvat equations is constant acceleration. The velocity, at a certain point can be constant, which is the scenario given here v = 16, is only true at t = 4, and if we go to t = 4.001, it's no longer true. make sense now?

Reply 8

username1393226

OP

2

Original post by devangdave

The required state to use the suvat equations is constant acceleration. The velocity, at a certain point can be constant, which is the scenario given here v = 16, is only true at t = 4, and if we go to t = 4.001, it's no longer true. make sense now?

Understood. Thanks.

[Mechanics] Questions using Suvat equations (motion equations)

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