Question

True or false: When a bullet is fired horizontally, it takes the same amount of time to reach the ground as a bullet dropped from rest from the same height.

Why?

Answer 1

True

Answer 2

Because the initial vertical component of a bullet's velocity is 0 in both cases

Answer 3

Officially:"The x and y components of the motion of ANYTHING is independent"

What does this MEAN?

Take any particle or body or whatever and apply a force onto it with x and y components. The force and resulting motion in the x direction is exactly the same if you just applied the x component of that force in the x direction. It's like 2 different worlds are in motion at once.

Answer 4

Of course in 3D, that would be 3 worlds.

Answer 5

Basically if you drop the bullet, then Vi = 0
Viy = ViSin(theta) = 0*Sin(theta) = 0

If you shoot it horizontally, then theta=0, so
Viy = ViSin(theta) = Vi * Sin0 = Vi* 0 = 0

Answer 6

so in the Y direction of motion there is only gravity acting on the bullet, in the first case, the velocity is inthe X direction so its only important for the Range but not the height and the gravity alone acts on the bullet on hte Y axis, and in hte free fall gravity os the only thing acting on it regardless if there is motion in the x or not

Answer 7

Or: if you projected a shadow from the x-y plane onto just the x plane, you wouldn't be able to tell (with forces and momentum) what was going on in the y-direction (although in practice you could make a guess, as the 'energy' of the shadows aren't conserved, but oh well)

Answer 8

so True of course!!!

Answer 9

Hmm... Interesting. Thanks for the answers!

Answer 10

http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-3/
watch from 44:45