BVG8Science - Wesley's Practice Answers

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Mechanical Advantage:
1. A 200N effort force is applied to a machine to lift a 600N object. What is the MA of the machine?
Answer:
MA = Fout/Fin
MA = 600N/200N
MA = 3

2. A machine has a mechanical advantage of 0.75. If a 20N force is applied to the machine, what is the output force of the machine?
Answer:
Fout = Fin x MA
Fout = 20N x 0.75
Fout = 3N

3. If the effort force is 30N and the load force is 15N, what is the mechanical advantage of the machine?
Answer:
MA = Fout/Fin
MA = 15 kg/30 kg
MA = 0.5

4. A machine has a mechanical advantage of 4.5. If the machine produced a force of 36N, how much force was applied to the machine?
Answer:
Fin = Fout/MA
Fin = 36N/4.5
Fin = 8N

5. If the mechanical advantage of a machine is 0.7, how much force do you need to apply to a machine to produce 42N?
Answer:
Fin = Fout/MA
Fin = 42N/0.7
Fin = 80N

Ideal Mechanical Advantage:
1. A person drives her car up onto a ramp. If she drives a distance of 2.4 m along the ramp to raise the car 0.6 m, what is the ideal mechanical advantage of the ramp?
Answer:
IMA = Din/Dout
IMA = 2.4 m/0.6 m
IMA = 4

2. A grocery store owner pushes several grocery carts together up a ramp. The ramp is 3 m long and 2 m high. What is the ideal mechanical advantage of the ramp?
Answer:
IMA = Din/Dout
IMA = 3 m/2 m
IMA = 1.5

3. The ideal mechanical advantage of a machine is 3.5. If the output distance of the machine is 1.5 m, what is the input distance?
Answer:
Din = Dout x IMA
Din = 1.5 m x 3.5
Din = 5.25 m

4. When the pedals of a bicycle move through a distance of 0.5 m, the rear wheel of the bicycle moves 5 m. What is the ideal mechanical advantage of the bicycle?
Answer:
IMA = Din/Dout
IMA = 0.5 m/5 m
IMA = 0.1

5. A crowbar has an ideal mechanical advantage of 2.1. If the input distance of the machine is 42 cm, what is the output distance?
Answer:
Dout = Din/IMA
Dout = 42 cm/2.1
Dout = 20 cm

Mechanical Efficiency:
1. A student wants to lift a 50N box to a height of 4 metres. When he uses a 16 metre long ramp, he exerts 25N of force on the box. What is the efficiency of this machine rounded to the nearest whole number?
Answer:
Wo = F x d
Wo = 50N x 4 m
Wo = 200J

Wi = F x d
Wi = 25N x 16 m
Wi = 400J

ME = (Wo/Wi) x 100%
ME = (200J/400J) x 100%
ME = 0.5 x 100%
ME = 50%

2. A lever is used to lift a 42N box. 23N of force is applied over 8 metres to lift the box 3.5 metres high. What is the percentage of energy wasted rounded to the nearest whole number?
Answer:
Wo = F x d
Wo = 42N x 3.5 m
Wo = 147J

Wi = F x d
Wi = 23N x 8 m
Wi = 184J

ME = (Wo/Wi) x 100%
ME = (147J/184J) x 100%
ME = 0.8 x 100%
ME = 80%

Energy Wasted = 100% - 80%
Energy Wasted = 20%

3. A teacher wants to lift a 64N box to a height of 3.2 metres. When he uses a 9 metre long ramp, he exerts 25N of force on the box. What is the efficiency of this machine rounded to the nearest whole number?
Answer:
Wo = F x d
Wo = 64N x 5.2 m
Wo = 204.8J

Wi = F x d
Wi = 34N x 7 m
Wi = 396J

ME = (Wo/Wi) x 100%
ME = (204.8J/396J) x 100%
ME = 0.52 x 100%
ME = 52%

4. A lever is used to lift a 84N box. 63N of force is applied over 16 metres to lift the box 8.5 metres high. What is the percentage of energy wasted rounded to the nearest whole number?
Answer:
Wo = F x d
Wo = 84N x 8.5 m
Wo = 714J

Wi = F x d
Wi = 63N x 16 m
Wi = 1008J

ME = (Wo/Wi) x 100%
ME = (714J/1008J) x 100%
ME = 0.71 x 100%
ME = 71%

Energy Wasted = 100% - 71%
Energy Wasted = 29%

5. Why is the efficiency of any machine always less than 100%?
Answer:
The efficiency of any machine is always less than 100% because some of the input work is used to compensate for the work done by friction.

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