Mechanical Advantage & Efficiency of Incline Planes (pages 110 & 112 in textbook)
1. Draw a picture of an incline plane. Label the input force and output force. What is
the ideal mechanical advantage of an incline plane?
input force →
↑ output force; output force/input force = MA
or, length of ramp/ ht. of ramp
2. What is the formula for mechanical advantage (page 105)? What is the mechanical
advantage of a incline plane (ramp) of height 10 m and length 60 m?
mechanical advantage = output force/ input force; 60 m/10m = 6
3. What is the formula for efficiency (page 107)? Why is input work always greater than
output work? Actual efficiency of a machine is always less than__________%.
output work / input work x 100 % = efficiency; friction; 100
4. If you lift a box with a force of 100 N and you can push a box to the same height
using an incline plane with only 10 N what is the mechanical advantage of the incline
plane?
MA = output force/input force = 100 N/ 10 N = 10
5. If a box has a mass of 100 kg and you want to lift it to a height of 10 m with a
incline plane, what would the output force of such an incline plane be? (hint: the
acceleration due to gravity is approximately 10 m/s2)
100 kg x 10 m/s2 x 10 m = 10,000 joules of work required,
so, 10,000 joules / 10 m = 1,000 N (Joules = N x m)
6. A ramp (incline plane) requires 5,000 joules of input work and 1,000 joules of output
work. What is the ramp’s efficiency?
Efficiency = output work / input work x 100% so, 1,000 J / 5,000 J x 100% = 20 %
7. If you push a box up a ramp 10 m with a force of 10 N to a height of 1 m, and you lift
the same box 1 m with a force of 10 N, what is the efficiency of the ramp?
(hint: Write the formula for efficiency. Then figure the output work and the input
work for both cases above.)
Efficiency = output work / input work x 100%, Work (J) = N x m, so…
input work = 10 N x 10 m = 100 J
output work = 10 N x 1 m = 10 J
Efficiency = 10 J / 100 J x 100% = 10%
8. Thought Question: A lever is a more efficient machine because it is less affected by
_____________________ (fill in the blank).
(friction)