Which statement best describes why a machine is useful? a machine does a greater amount of work than the amount of work that is done on it. a machine does a smaller amount of work than the amount of work that is done on it. a machine can decrease both the input force and the input distance needed to do a given amount of work. a machine can decrease either the input force or the input distance needed to do a given amount of work.

"A machine can decrease either the input force or the input distance needed to do a given amount of work" is the best statement that describes why a machine is useful.

Option D

Explanation :

A machine is simply defined as a device that helps humans, helping them to transfer the required amount of force to compete any task, changing the direction of motion, increasing the magnitude of force to complete any task, reduce the time or distance needed to cover while performing any task.

Machines can be simple mechanical device or a combination of multiple mechanical or technical devices to reduce the amount of input force or increase the output.

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current

he would use the colour black