Position of Object Dropping from 100 ft: t=0, x=0?

[foo9008]

Homework Statement

for part b , why when t = 0 , x= 0 , why not x =100 ? the author gave that the object drop from height of 100ft at the start of the question.

Homework Equations

The Attempt at a Solution

 

[Mark44]

Homework Statement

for part b , why when t = 0 , x= 0 , why not x =100 ? the author gave that the object drop from height of 100ft at the start of the question.

Homework Equations

The Attempt at a Solution

The author is defining the point at which the object is dropped as x = 0, and the point on the ground as x = 100.

 

[foo9008]

The author is defining the point at which the object is dropped as x = 0, and the point on the ground as x = 100.

Is it wrong to consider x=100 when t=0??

 

[Mark44]

Is it wrong to consider x=100 when t=0??

Yes, if you're trying to follow the author's work.

 

[HallsofIvy]

There are no "coordinates", x, y, t, etc. automatically given by a physical situation- you define those yourself. Here, where we have an object dropped from a height we can choose to take x to be 0 at the ground, in which case x(0)= 100, or we can choose to take the x to be 0 at the point from which the object was dropped so that x(0)= 0. We can also choose in which direction to take x to be positive or negative.