UVAST and constant acceleration

graate

Hey everyone,

here's hoping somebody could give me a hand with this physics question that I can't get my button around.

A car travelling with a constant acceleration has a velocity of 6ms^-1 at a given instant. In the next minute it travels 3 km. Find its acceleration and the velocity after one minute.

So what I'm not sure about is the "given instant" part. Is that basically initial velocity? If so should I not use the formula s=ut + 1/2at^2 ? When I do this I get the answer 1.3888 ms^-2 but the book has the answer 1.467ms^-2.

EDIT:

Another Q:

A car travels a distance of 200m as its speed changes from 30m/s to 10/s. Find its deceleration. What formula do I use here? I can't seem to figure this one out. Thanks!

What do you guys think?

Thanks!

citrus burst

graate wrote: »

Hey everyone,

here's hoping somebody could give me a hand with this physics question that I can't get my button around.

A car travelling with a constant acceleration has a velocity of 6ms^-1 at a given instant. In the next minute it travels 3 km. Find its acceleration and the velocity after one minute.

So what I'm not sure about is the "given instant" part. Is that basically initial velocity? If so should I not use the formula s=ut + 1/2at^2 ? When I do this I get the answer 1.3888 ms^-2 but the book has the answer 1.467ms^-2.

EDIT:

Another Q:

A car travels a distance of 200m as its speed changes from 30m/s to 10/s. Find its deceleration. What formula do I use here? I can't seem to figure this one out. Thanks!

What do you guys think?

Thanks!

The trick, I found while doing these type of questions, is to write down all the information you are given and leave a question mark beside ones you don't have. All other information is pretty much irrelevant. In this case:

u = 6 m/s
v = ?
a = ?
s = 3000
t = 60

You used the equation s = ut + 0.5at^2 and solved for a

a = 2(s - ut)/t^2

so as long as that equation is right and you sub in the correct values you should get an answer of 1.4667 m/s/s. As far as I can see you either made a computation mistake or didn't solve for a correctly.

for the 2nd Q again write out your information

u = 30
v = 10
a = ?
s = 200
t = doesn't matter, not given in the question

So you can see now that you don't need to worry about t, this question becomes pretty simple. The only equation you can use is:

v^2 = u^2 + 2as

Rearranging for a gives:

a = (v^2 - u^2)/2s

Try it yourself, it should work out

graate

citrus burst wrote: »

The trick, I found while doing these type of questions, is to write down all the information you are given and leave a question mark beside ones you don't have. All other information is pretty much irrelevant. In this case:

u = 6 m/s
v = ?
a = ?
s = 3000
t = 60

You used the equation s = ut + 0.5at^2 and solved for a

a = 2(s - ut)/t^2

so as long as that equation is right and you sub in the correct values you should get an answer of 1.4667 m/s/s. As far as I can see you either made a computation mistake or didn't solve for a correctly.

for the 2nd Q again write out your information

u = 30
v = 10
a = ?
s = 200
t = doesn't matter, not given in the question

So you can see now that you don't need to worry about t, this question becomes pretty simple. The only equation you can use is:

v^2 = u^2 + 2as

Rearranging for a gives:

a = (v^2 - u^2)/2s

Try it yourself, it should work out

Thanks mate finally got it! Thanks a bunch.. On to Velocity time graphs and Gravity!