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October 25th, 2007, 07:54 PM   #1
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Force and Motion

1. A box with mass of 50.0 kg is placed on the floor of an elevator. What force does the box exert on the floor when the elevator is accelerating upward at the rate of 2.0 m/sec^2? When it is accelerating downward at the rate of 3.0 m/sec^2?
2. A rifle bullet leaves the muzzle of a gun at 800 m/sec. The rifle barrel is 80 cm long, and mass of the bullet is 200 g. What force was needed to accelerate the bullet?

Well, the two questions above were the ones that I need help on.
Currently, I'm learning about force and motion. I know that F=ma, but I forgot about the types of forces, and other basic mathematical equations for force and motion topic. I would appreciate if anyone help me on this.

Thanks,

J.
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October 26th, 2007, 06:39 PM   #2
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Quote:
1. A box with mass of 50.0 kg is placed on the floor of an elevator. What force does the box exert on the floor when the elevator is accelerating upward at the rate of 2.0 m/sec^2? When it is accelerating downward at the rate of 3.0 m/sec^2?
Well, the force downwards on the floor will equal the usual weight of the box (mass*acceleration due to gravity) plus the mass of the box multiplied by its acceleration upwards, because F = ma.


Quote:
2. A rifle bullet leaves the muzzle of a gun at 800 m/sec. The rifle barrel is 80 cm long, and mass of the bullet is 200 g. What force was needed to accelerate the bullet?
F = ma, so the force needed is the mass of the bullet multiplied by the acceleration. Assuming an average acceleration, the acceleration would be the final velocity minus the initial velocity divided by the time over which it took to change from the initial to the final velocity.
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October 26th, 2007, 07:22 PM   #3
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Thanks for the reply.
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