Select all the correct definitions
a. mechanical advantage is the ratio of output force/ input force
b. mechanical advantage is the ratio of input/output force
c. efficiency is the ratio of input work/ output work expressed as a percentage
d. efficiency is the ratio of output work/input work expressed as a percentage

b and d

Explanation:

Mechanical advantage:  It is ratio of output force and input force.  

Efficiency: It is ratio of output work and input work expressed as a percentage.

Option A and D

Explanation:

A mechanical advantage is defined as the ratio of output force to the input force. No units are there for the mechanical advantage. Based on the Law of conversation of energy, the energy cannot be multiplied. Efficiency is being defined as the effect of the device on the output work. It is represented as a percent.

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.