An elevator is lifted up by a thick steel cable. While the elevator is moving upwards with a decreasing velocity,
a. the upward force on the elevator by the cable is greater than the downward force of the Earth
b. the amount of upward force due to the cable is equal to the amount of the downwards force due to the Earth
c. the upwards force of the elevator is less than the downwards force of the Earth
d. The Earth pulls less on the elevator while its in motion then when it is at rest
If the upward force were greater than m g, the car would accelerate UP, a - no
If they were equal, constant velocity would result, b - no
it is deaccelerating, c - yes
d. is simply nonsense
To understand the situation, we need to consider the different forces acting on the elevator:
1. Weight or the downward force due to gravity: This force is exerted by the Earth and acts downwards. It is given by the equation F = mg, where m is the mass of the elevator and g is the acceleration due to gravity.
2. Tension in the cable: The steel cable supports the elevator and exerts an upward force to counterbalance the weight. This force is often referred to as tension.
Now, let's analyze each option:
a. The upward force on the elevator by the cable is greater than the downward force of the Earth: This option is incorrect. If the upward force were greater than the downward force, the elevator would be accelerating upwards, not moving with a decreasing velocity.
b. The amount of upward force due to the cable is equal to the amount of the downward force due to the Earth: This option is also incorrect. If the upward force and the downward force were equal, the elevator would be at a constant velocity, not decreasing.
c. The upwards force of the elevator is less than the downward force of the Earth: This option is correct. Since the elevator is moving upwards with a decreasing velocity, the upward force (tension) exerted by the cable is less than the downward force (weight) due to the Earth. The net force in the upward direction is smaller than the net force in the downward direction.
d. The Earth pulls less on the elevator while it's in motion than when it is at rest: This option is incorrect. The force of gravity acting on the elevator remains the same regardless of its motion. The weight of the elevator, which is determined by its mass and the acceleration due to gravity, is constant.
So, the correct option is c. The upwards force of the elevator is less than the downwards force of the Earth.