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

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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

 

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foo9008 said:

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.
 
Mark44 said:
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??
 
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.