When using a real machine to do work, input work will always be

Explanation:

In physics, simple machines must have a efficiency rate that is measured depending on how much energy needs to work, and how much energy is released (input - output).

In real machines, to have efficiency they must do work with less energy possible. So, good efficiency in real ones should imply that input work is less than output work, because in the other way machines don't make sense.

For example, steam locomotive, imagine that the input work is the same as output work. This situation don't make sense, because is impossible for a human being to do that, it requires to much effort.

So, the sense of a machine is that input work is less than output work.

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.

can be answered using momentum.

momentum = p

p1= mass1 * velocity1

p1 = p2

therefore

p1 = 6kg * 4m/s

p1 = 24kgm/s

p2=m2 * v2

24 kgm/s = 7kg * v2

v2 = 24 kgm/s / 7kg

v2= 3.42 m/s