A student drops his textbook out of a window in a tall building. How high above the ground is the book when it is falling at a speed of 438 cm/s?

2 Answers
A08
Feb 17, 2018

It is presumed that the given falling speed of book just is as it hits the ground.

Explanation:

Applicable kinematic expression is

v^2-u^2=2gh

Inserting given values in SI units we get

(4.38)^2-(0)^2=2xx9.81xxh
=>h=(4.38)^2/(2xx9.81)=97.7\ cm

Height given in cm as speed given in cms^-1

A08
Feb 24, 2018

Alternate solution.

Explanation:

Let height of the window be =h\ m above the ground.
Let the book be at a height h_1\ m above ground when the desired speed is achieved.
Let the student drop the book with initial velocity =0

For free fall under gravity applicable kinematic expression is

v^2-u^2=2gs

Inserting given values in SI units we get

(4.38)^2-(0)^2=2xx9.81xx(h-h_1)
=>(h-h_1)=(4.38)^2/(2xx9.81)
=>(h-h_1)=0.98
=>h_1=0.98-h\ m

Related questions
See all questions in Falling Objects
Impact of this question
2893 views around the world
You can reuse this answer
Creative Commons License