Physics question on motion

einstein101

1. The problem statement, all variables and given/known data
An object that is acclerating uniformly travels 22.5 m in the eighth second of its motion.
a) what is the acceleration of the object?

b) how far does the object travel in 6 seconds?


2. Relevant equations
I'm not exactly sure what equation would be necessary-
perhaps -- a=v-u/t
v=u+at
x=ut+1/2at^2


3. The attempt at a solution

i attempted to use the a=v-u/t equation, however, it wasn't successful. I don't even think you can use that equation since we dont have the values for velocity;initial nor final.

PhanthomJay

The object has no motion at t = 0. How far does it travel in 8 seconds? How far does it travel in 7 seconds? Its displacement between the. 7th and 8th seconds is given as 22.5 m. Use your last equation.

NascentOxygen

Hi einstein101. The eighth second is that time difference between seven seconds and eight seconds.

travel during first 7 seconds= u.7 + (1/2)a.7²

travel during first 8 seconds= ????

einstein101

But how do I find the initial velocity for the equation?
And how would I exactly go about finding the acceleration?

e^(i Pi)+1=0

It says nowhere that the object started from rest.

Doc Al

It says "in the eighth second of its motion". I would interpret that to mean that it started from rest.

NascentOxygen

Can you finish the equation I left uncompleted?

e^(i Pi)+1=0

Hmm, I suppose you're right.

einstein101

so travel during first 8 seconds=u x 8 +1/2(a)(8)^2

then what do i do?

NascentOxygen

Good. Now subtract that from the companion equation I gave you, viz., of distance travelled during first 7 seconds.

PhanthomJay

It has been established that the object starts from rest and thus u = 0 and the distance traveled in 8 seconds is 32(a). In a similar manner, find the distance traveled in 7 seconds. Subtract this 2nd equation from the first equation and set the result equal to 22.5 to solve for a.