Turning effect (Lever, Pulley, and Inclined Plane) Worksheet and Answer For Junior High School

1.First class lever has a 4900N weight located 4 meters from the fulcrum. If the force is applied 8 meters from the fulcrum, how much force is needed?

Known:w = 4900 N
l_A = 4 m (distance beetwen weight and pivot)
E_A = 8 m (distance beetwen force and pivot)
Asked: F?
Answer: w . l_A = F . E_A 4900 N . 4 m = F . 8 m
F = ^{4900 N . 4 m} / _{8 m}
F = 2450 Newton

2.Second class lever has a 19600N weight located 4 meters from the fulcrum.  If the lever is 10 meters long, how much force must be applied at the other end to lift the weight?

Known:w = 19600 N
l_A = 4 m (distance beetwen weight and pivot)
For second class lever:
Length of lever = E_A = 10 m (distance beetwen force and pivot)
Asked: F?
Answer: w . l_A = F . E_A 19600 N . 4 m = F . 10 m
F = ^{4900 N . 4 m} / _{8 m}
F = 7840 Newton

3. A third class lever is 4.8 meters long. The fulcrum is at one end. The force is applied 3.0 meters from the fulcrum.  How much force will it take to lift a weight of 160 N?

Known:w = 160 N
For third class lever:
Length of lever = l_A = 4.8 m (distance beetwen weight and pivot)
E_A = 3 m (distance beetwen force and pivot)
Asked: F?
Answer: w . l_A = F . E_A
160 N . 4.8 m = F . 3 m
F = ^{160 N . 4.8 m} / _{3 m}
F = 256 Newton

4. Two boys take a 12 m long board and rest it on a large rock to make a teeter-totter. If the 50 kg boy sits x m from the fulcrum, how far must the 70 kg boy sits from the fulcrum if they balance? (hint: use the 50 kg boy as output/object)

Known:
Length of lever = 12 m
the 50 kg boy as output/object)
w = 50 x 10 = 500 N
F = 70 x 10 = 700 N
l_A = x m (distance beetwen weight and pivot)
E_A = (12 - x) m (distance beetwen force and pivot)
Asked: E_A?
Answer: w . l_A = F . E_A
500 N . x m = 700 N . (12 - x) m
500x = 8400 - 700x
700x + 500x = 8400
1200x = 8400
x = 8400/1200 x = 7 m So, E_A = (12 - x) m (distance beetwen force and pivot)
= 12- 7
= 5 m

5. The man is lifting a box, it has mass 400 kg, how much force does the man need to apply to lift box?

Known:
mass of box = 40 kg, so weight = 40 x 10 = 400 N
Asked: F?
Answer: The mechanical advantages of pulley on that picture is 2 ( based on numbers of pulleys)
MA = W/F
2 = 400 / F
F = 400 / 2
F = 200 N

6. What is the MA of this ramp? Show your work.
a). Calculate the MA
b). Calculate the force do we need to apply to the box

Known:
mass of box = 100 kg, so weight = 100 x 10 = 1000 N
Base of inclined plane = 12 m
Slope of Inclined plane = 15 m
Asked: a). MA?
b). F?
Answer:
a). MA = s/h
We find the height using pythagorean theorm; a² + b² = c²
h²=s² - b²
= 15² - 12²
= 225 - 144
= 81
h = 81^1/2
h = 9 m,
MA = 15 / 9
= 1.67
b).MA = w/F
15/9 = 1000 / F
F = 600 N