why can't a machine work as a force and a speed multiplier simultaneously?justify.

It is not possible to increase speed and foece at the same time because only one quanitity can be increased to affect the other quantity.

For example: In case of a wheel, if the rim of the wheel is turned then the axle at the center turns with less speed but more force. Thus, the wheel works as a force multiplier. If you turn the axle only then the wheel becomes the speed multiplier. This is because the axle turns a short distance and the outer rim of the wheel turns much further. This is how the wheel moves faster.