Physics True/False?

Question

My answers seemed to throw ppl off, here's the clean version: Can someone help me with the reasoning, True/False?

A) The kinetic energy of an object depends on the direction of the motion involved.
B) The kinetic energy can never be negative.
C) The work done by a constant force acting on an object is independent of the orientation of the force relative to the motion of the object
D) The work-energy principle is not valid if there are frictional forces acting.
E) Work cannot be done in the absence of motion.
F) The work done to raise a box onto a platform depends on how fast it is raised. (Neglect friction, assume it starts on the ground at rest, and ends up resting on the platform)

Answer 1

A) FALSE:

Energy does not depend on the direction. Energy is calculated via the equation: E = 1/2mv^2. This formula does not account for direction at all...simply speed and mass.

B) TRUE: Energy is never negative. (Some odd physicists have tried to show that in certain cases, energy is negative, but that's not the case.) Work, on the other hand, can have a negative value.

C) FALSE: "The word done by a constant force acting on an object..." (Let's imagine that is gravity). "...is independent of the" (doesn't matter--i.e. is not affected by)..."the force relative to the motion of the object." (Like the pushing force behind a toy car).
Your kid pushes a car with a force "F". The force of gravity will not change (is constant) and is not affected by this force--the force relative to the motion of the vehicle. So question "C" is true.



D) TRUE: The work-energy principle is not valid unless it is in an isolated system. Isolated meaning free from friction, gravity etc. That's why on physics tests they'll say stuff like "Assume that friction is negligible" or "Ignoring the effects of friction"

E) TRUE: If you just push on a door as hard as you can, and the door doesn't move, you haven't done any work. The door would have to move for work to be done.

F) TRUE: Force is change in momentum over change in time, and momentum is defined by velocity. If you move it faster it requires more force. More force will equate to more work.

Answer 2

a million. think of of intense tension wires for the transmission of electric energy. 2. Q: If 2 gadgets have the comparable mass, how can certainly one of them be greater great? greater great potential "has greater mass."