A) If the moon revolves around the earth in a perfectly circularorbit, then the

Question

A) If the moon revolves around the earth in a perfectly circularorbit, then the earth does not do any work on the moon.
B) The kinetic energy of an object depends on the direction of themotion involved.
C) An object moves through various altitudes such that it ends inthe same place it started. The total work done by the weight duringthis motion is zero.
D) Work can be done in the absence of motion.
E) The work done to raise a box onto a platform does not depend onhow fast it is raised.
F) The kinetic energy can be negative.

I strongly feelB=False,C=True,D=False,E=True,bot not 100%. I'm unsure of A &F. Any help would be appreciated.

Explanation / Answer

The answers seem to alternate. It should be: A) True B) False C) True D) False E) True F) False Here's my reasoning: A) By definition, work(W) done on an object is defined as the force(F)acting on the object over a displacement(x). The force must be inparellel to the displacement so it can be useful to remember workby the following equation: W = F*xcos() where is the angle between the force and the displacementvector. If the moon had a perfectly circular orbit, thedisplacement vector of the moon would always be perpendicular tothe force vector and cos(90) is zero. Due to this fact, no work isevery done on the moon by the Earth. B and F) K = 1/2 mv2 ; Whether velocity is defined to be positive or negative, the valueof velocity is always squared and will always yield a value for Kgreater than or equal to zero. **However** It is possible for the change in kinetic energy to benegative. If you have a ball rolling with some initial velocity,v0 that comes to rest, you end up getting a negativechange in kinetic energy. C) Work is not dependent on the path taken. What matters is where anobject starts and where it finishes. Because the net displacementis zero, work is also equal to zero. D) If there is no motion, there cannot be work. There can be aconstant force being applied, such as when you hold a 5lb weight infront of you for awhile. However, work is a force applied over adisplacement so no displacement, no work. E) W = F*xcos(). No time variable is present, therefore, thework done to raise a box onto a platform does not depend on howfast it is raised. I hope this helps.

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