The force of gravity is twice as large on a 2kg rock as it is on a 1 kg rock. Ho

Question

The force of gravity is twice as large on a 2kg rock as it is on a 1 kg rock. However, if both rocks are dropped to the ground, they experience the same acceleration. Explain. Two constant forces of equal magnitude begin to act on a previously moving object. What configuration or relative configuration of the two force directions is needed for the object to continue moving at its previous velocity? (Hint: Newton's 2nd Law) Explain. An elevator with a person in it is being pulled upwards by a cable. Identify all interaction forces (Newton's 3 Law) in the system. Specify the object the force acts on and the direction of the force. Consider your system to consist of the cable, the elevator, the Earth and the person. For example, the Earth pulls down on the elevator with force Mg and the elevator pulls up on the Earth with force Mg. There are four more pairs of forces.

Explanation / Answer

1. the acceleration is force/mass.

force on 1 kg = 9.8 N; acceleration = 9.8/1 = 9.8

force on 2 kg = 9.8*2 N; acceleration = 9.8*2/2 = 9.8

2.the forces should be at 180 degrees to each other, so that, the resultant force can be zero, according to the law of superposition of forces.

3.

a. the earth pulls down the preson downwards with force Mg (M=mass of person)

b. The cable has a tension acting away from the elevator (up)

c. if the elevator is accelerating, then there's a pseudo force acting on the man, = Ma where +a is the upwards acceleration of the lift.

d. there's normal reaction from the elevator's floor (upwards) = (Ma + Mg) if accelerating, Mg otherwise.

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