## homework - past paper questions

### claribell

Posted 09 January 2007 - 05:11 PM

this is probably a really simple question but im a bit stuck with what equation to use so can someone please tell me what equations to use so i can attempt it.

a sports car is being tested along a straight track

i)in the first test the car starts from rest and has a constant acceleration of 4m/sē in a straight line for 7.0 seconds.

calculate the distance the car travels in the 7 seconds.

ii)in a second test the car again starts from rest and accelerates at 4m/sē over twice the distance covered in the first test.

what is the increase in the final speed of the car at the end of the final test compared with the final speed at the end of the first test?

iii) in a third test the car reaches a speed of 40m/s. it then decelerates at 2.5m/sē until it comes to rest.

calculate the distance travelled by the car while it decelerates to rest

### dfx

Posted 09 January 2007 - 05:36 PM

i) SUVAT equations, straightforward plugging in of the values, solve for S.
ii) Knowing S, SUVAT again and solve for V.

Hold on that that V, let's call it Vii. Go back to (i) and solve V this time, and let's call the V from (i) um how about Vi. That gives you your 2 final velocities for the 2 situations, subtract Vi from Vii and you get the amount by which Vii is greater.

(iii) SUVAT is today's magic word yet again. You know your u, your v is zero, given a (remember its a negative value), solve for s.

Good luck and post back if that's vague, but it is reasonably straightforward.

### claribell

Posted 09 January 2007 - 05:51 PM

for (i) i got 98m so for the displacement in (ii) do i double the displacement from (i) to make s=196m ?

thank you for your help i cant believe how simple it was just needed the magic word SUVAT hehe

### John

Posted 09 January 2007 - 09:35 PM

QUOTE(dfx @ Jan 9 2007, 05:36 PM)

i) SUVAT equations, straightforward plugging in of the values, solve for S.
ii) Knowing S, SUVAT again and solve for V.

Hold on that that V, let's call it Vii. Go back to (i) and solve V this time, and let's call the V from (i) um how about Vi. That gives you your 2 final velocities for the 2 situations, subtract Vi from Vii and you get the amount by which Vii is greater.

(iii) SUVAT is today's magic word yet again. You know your u, your v is zero, given a (remember its a negative value), solve for s.

Good luck and post back if that's vague, but it is reasonably straightforward.

Christ, I have a B in Higher Physics and have no idea what you said lol, SUVAT?

### claribell

Posted 09 January 2007 - 09:42 PM

Christ, I have a B in Higher Physics and have no idea what you said lol, SUVAT?
[/quote]

its the vertical components some people use

U=initial velocity
V=final velocity
A=acceleration
S=displacement
T=time

by any chance can you help me with my other homework question that i posted?
its from a past paper not sure which one teacher just made a booklet with past paper questions in it.if not then its cool.

### John

Posted 09 January 2007 - 09:50 PM

[quote name='claribell' date='Jan 9 2007, 09:42 PM' post='92624']
Christ, I have a B in Higher Physics and have no idea what you said lol, SUVAT?
[/quote]

its the vertical components some people use

U=initial velocity
V=final velocity
A=acceleration
S=displacement
T=time

by any chance can you help me with my other homework question that i posted?
its from a past paper not sure which one teacher just made a booklet with past paper questions in it.if not then its cool.
[/quote]

Ah i thought there was more to it, such as leading to a formula lol, i'll take a look at the question and see if i remember how to do it, been nearly 2 years since i last did physics

### claribell

Posted 09 January 2007 - 09:51 PM

thank you much appreciated

### dfx

Posted 09 January 2007 - 11:12 PM

QUOTE(claribell @ Jan 9 2007, 05:51 PM)

for (i) i got 98m so for the displacement in (ii) do i double the displacement from (i) to make s=196m ?

Yes, that's correct, as it says s is doubled.

QUOTE(John @ Jan 9 2007, 09:35 PM)

Christ, I have a B in Higher Physics and have no idea what you said lol, SUVAT?

Evidently not.

### Flyer

Posted 03 February 2007 - 09:47 PM

Just remember the basic formula

v = u+at
s = ut+1/2at^2
v^2 = u^2+2as (remember to square root the answer)

Where

v = final velocity
u = starting velocity
s = displacement
a = acceleration
t = time