Question

A physics teacher is walking at a constant speed at 2 m/s towards the door of a 25 m high building. A student at the top of the building wants to hit the head of the physics teacher w/ a book. At what distance the teacher be, the student will drop the book so that it will be exactly on the teacher's head?

Answer 1

First you need to find the time it takes for the book to fall to the ground, using \[\Large h = 0.5 g t^2\]
h=25m, g is gravity (9.8m/s or 10m/s if you want to round it), find t.

Answer 2

Once you have t, use it to find how far away the teacher needs to be.

Answer 3

seriously hitting a teacher with a book :)

Answer 4

25m is pretty high to drop a book on someone... the book will be travelling ~80km/h or 50mi/h

Answer 5

@agent0smith where did you get 0.5?

Answer 6

Because that's what the equation is for height of a falling object. Half times gravity times time squared.

Answer 7

Oh, ok. What would be the equation to be used for finding the time since it's not given?

Answer 8

I gave you the equation to find the time, in the first response. Plug in the numbers and find t.

Answer 9

You'll have to rearrange it a bit to find t.

Answer 10

t^2=5.1 is it correct?

Answer 11

t=2.26

Answer 12

Yep.

Answer 13

What should I do next?

Answer 14

Now find the distance the teacher needs to be, using distance = speed*time. You know the time and his speed.

Answer 15

d= 4.52

Answer 16

@agent0smith thanks!