Ahand lifts a block vertically upward at constant velocity. the work done by gravity on the block if the system consists of the block only. and why?
a) is zero,
b) is zero/is zero,
c) is negative/is zero,
d) is positive/is negative,
e) is negative/is positive,
f) is positive

1) when you rub your hands together quickly, the kinetic energy is converted to mechanical energy.2) thermal energy from the sun travels to earth as infrared waves.3) energy is transferred through the matter of space by electromagnetic waves. 4) when a match is burned, chemical potential energy is converted to thermal and radiant energy. 5) seismicwaves are caused by back and forth movement , or vibration, of an object. 6) mechanicalenergy in an engine changes thermal energy into kinetic energy to make a car move.

The answer is frictional force