The efficiency of the ramp can be improved by smoothening the surface. The correct option is D.) Smooth the surface
Efficiency
Efficiency is the percent of work put into a machine by the user that becomes work done by the machine.
It could also be defined as the percentage ratio of the output energy to the input energy.
The closer to 100 percent a machine’s efficiency is, the better it is at reducing friction.
Therefore, a surface that would provide a lower friction would increase the efficiency of the ramp.
A smooth surface reduces friction.
Hence, the efficiency of the ramp can be improved by smoothening the surface. The correct option is D.) Smooth the surface
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