# HELP : Q12 of Ch. 02 of Fundamentals of Physics, Resnick

1. Nov 22, 2009

### dawoodvora

1. The problem statement, all variables and given/known data
A rapidly growing plant doubles in height each week. At the end of the 25th day, the plant reaches the height of a building. At what time was the plant one-fourth the height of the building?

2. Relevant equations
The problem is a part of chapter which deals only with linear kinematics. But I cannot understand, which part of 4, general kinematic equation, I must apply.

3. The attempt at a solution
It looks like a case of geometric progression, But I am not able to get a start
Also, I tried to start it by actually creating a table where there are three columns.
column 1 = no. of weeks
column 2 = initial height
column 3 = final height.

After that I drew blank..............

2. Nov 22, 2009

### Staff: Mentor

Work backwards from the time that the plant was the height of the building. When was it 1/2 the height of the building? When was it 1/4 the height of the building?

This problem has nothing to do with kinematics.

3. Nov 22, 2009

### dawoodvora

Hello Mark44,
U r DAMN RIGHT!

Once, I saw through your eyes, the prob was as clear as water

On 25th day height is h
On (25-7)= 18, height will be h/2
On (18-7) = 11, height will be (h/2)/2 = h/4

Beauty.......................

ThnX...........................a LooooooooooooooooooooT