Tuesday, December 14, 2010

Do Not Try This at Home

A man holds a rifle horizontally 6 feet above the ground. At the moment he fires it, another bullet is dropped from the same height, 6 feet. Which bullet hits the ground first?

For the physics-minded among you, ignore friction and the curvature of the earth.


  1. Same time. Both have only gravity acting on them in the vertical direction.

  2. They will hit the ground at the same time. Because gavity is pulling downward on both bullits with the same force.

  3. Just out of curiosity, if we added back in the curvature of the earth and/or friction, anyone want to explain what would happen then?

  4. The curvature of the earth would not change the result because the earths gravitational field through which the bullets are falling is also curved. Friction between the bullets and the surounding air will cause the bullet with the highest velocity to fall slower if the shape of the bullet is such that the air causes a greater upward than downward acting force.

  5. It kind of depends on if the bullet that was fired strikes something, doesn't it? I mean...if it lodged in, say, a tree...the other bullet would beat it to the ground.

  6. Curvature will matter if the speed of fired bullet is high. In this case the height will increase because the level of ground will go down due to curvature.

    Moreover if the speed is greater than or equal to the escape velocity, the fired bullet will never come to the ground.


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