For each of the following statements determine whether it is correct or incorrect.
a. 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.
b. the work done to raise a box onto a platform depends on how fast it is raised.
c. the kinetic energy of an object depends on the direction of the motion involved.
d. the kinetic energy depends on the reference frame of the observer.
e. the kinetic energy is always positive.
f. if the earth revolves around the sun in a perfectly circular orbit, then the sun does not do any work on the earth.