Old professor question

[ICEMANSAV]

Once I was sat on a plane next to a prof and he set about setting me loads riddles. He said if you had an open field stretching for as far as you could see and had a pistol and a bullet at the same level ( i.e 5ft off the floor ) facing horizontal. If you fired the gun and dropped the bullet at exactly the same time from the same height which would hit the ground first? I said the bullet dropped by hand would be the first rather than the fired bullet, he told me no, they would hit the floor at exactly the same time? How?

[CT]

Ignoring factors like wind and such. Once it is fired the only forces acting on the bullets are gravity. Gravity is acting equally on both, therefore, they both accelerate towards the ground equally, hence hitting the ground at the same time. The horizontal velocity of the fired bullet is unaffected by gravity. Only the vertical velocity is changed by gravity acting on it.

[ICEMANSAV]

Would the force of gravity not be stronger however on an item going towards the core of earth than an item fired across from the force, or does this bear no meaning on the gravitational pull?

[Clanad]

CT is entirely correct, with the addition that the weight of the two objects makes no difference either.  An anvil dropped from the heighth of the muzzle at the exact instant the gun was fired would reach the earth at the same time as the bullet...

[CT]

In answer to your second post, the force of gravity acting on two objects at the equal height above the ground is the same. This is true no matter what its horzontal velocity. If your two objects were at different heights when they were released then they may travel the same distance downwards in different times. This is because the acceleration due to gravity increases, the closer to the centre of the earth you are.

[ICEMANSAV]

Thanks for the answers guys. In hindsight I should have simply talked to the man rather than feigning sleep!