Homework Help: physics

Posted by alexa on Saturday, July 2, 2011 at 1:48pm.

An elevator is being lifted up an elevator shaft at a constant speed by a steel cable. All fricional effects are negligible. In this situation,forces on the elevator are such that?:

A.the upward force by the cable is greater than the downward force of gravity
B. the upward force by the cable is smaller than the downward force of gravity
C.None of these: the elevator goes up because the cable is being shortened,not because an upward force is exerted on the elevator by the cable
D. the upward force of the cable is greater than the sum of the downward force of gravity and downward force due to the air
E. the upward force of the cable is equal to the downward force of gravity

Would it be choice A or C?

physics - Damon, Saturday, July 2, 2011 at 5:21pm
There is no acceleration up or down
F = m a
so
Net force is zero
m g down = cable tension up
so
E

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