Which of the following statements is true? A) The work done to raise a box onto

Question

Which of the following statements is true?

A) The work done to raise a box onto a platform depends on how fast it is raised.
B) The kinetic energy is independent of the reference frame of the observer.
C) Spring A and B are identical except that A is stiffer than B; that is kA > kB. More work must be expended on spring A if both springs are stretched by the same amount.
D) The kinetic energy of an object depends on the direction of the motion involved.
E) If the Earth revolves around the sun in a perfectly circular orbit, then the sun does work on the Earth.
F) The kinetic energy can never be negative.

Explanation / Answer

A)

False:

The work done to raise a box onto a platform = mgh

Where m=mass.g=gravity and h= height

Thus it is not depend on vvelocity

B)

False:

KE=1/2mv^2

V is the velocity of the object in reference frame of the observer. Hence KE is dependent on reference frame of the observer.

C)

True

WA=1/2*kA*x^2 and WB=1/2*kB*x^2

Since kA > kB => WA > WB

D)

True:

KE=1/2mv^2

V is the velocity of the object in reference frame of the observer. Hence KE is dependent on reference frame of the observer and thus direction.

E)

False:

If the orbit is circularforce of sun on the earth is perpendicular and instantaneous displacement of earth is perpendicular to this force. W=F.d =Fdcos=0

Thus W=0 is orbit is cicular.

F)

True:

KE=1/2*mv^2

M=mass and v=velocity

M and v^2 never be negative hence KE never be negative.

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