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
lA = 4 m (distance beetwen weight and pivot)
EA = 8 m (distance beetwen force and pivot)
Asked: F?
Answer: w . lA = F . EA
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
lA = 4 m (distance beetwen weight and pivot)
For second class lever:
Length of lever = EA = 10 m (distance beetwen force and pivot)
Asked: F?
Answer: w . lA = F . EA
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 = lA = 4.8 m (distance beetwen weight and pivot)
EA = 3 m (distance beetwen force and pivot)
Asked: F?
Answer: w . lA = F . EA
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
lA = x m (distance beetwen weight and pivot)
EA = (12 - x) m (distance beetwen force and pivot)
Asked: EA?
Answer: w . lA = F . EA
500 N . x m = 700 N . (12 - x) m
500x = 8400 - 700x
700x + 500x = 8400
1200x = 8400
x = 8400/1200
x = 7 m
So, EA = (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 = 811/2
h = 9 m,
MA = 15 / 9
= 1.67 b).MA = w/F
15/9 = 1000 / F
F = 600 N
1. You serve a volleyball with a mass of 2.1 kg. The ball leaves your hand with a speed of 30 m/s. The ball has ______________________ energy. Calculate it.
Kinetic
KE = 1/2 m v2
KE = 1/2 x 2.1 kg x (30 m/s)2
KE = 1/2 x 2.1 kg x 900 m2/s2
KE = 945 Joule
2. A baby carriage is sitting at the top of a hill that is 21 m high. The carriage with the baby weighs 12 N. The carriage has ____________ energy. Calculate it.
Gravitational Potential Energy
PE = m.g.h
note: weight = m. g =12 N
so put the weight directly to the equation below
PE = 12 N . 21 m
PE = 252 N.m
PE = 252 Joule
3. A car is traveling with a velocity of 40 m/s and has a mass of 1120 kg. The car has ___________energy. Calculate it.
Kinetic
KE = 1/2 m v2
KE = 1/2 x 1120 kg x (40 m/s)2
KE = 1/2 x 1120 kg x 1600 m2/s2
KE = 896,000 Joule
4. A cinder block is sitting on a platform 20 m high. It weighs 79 N. The block has _____________ energy. Calculate it.
Gravitational Potential Energy
PE = m.g.h
note: weight = m. g = 79 N
so put the weight directly to the equation below
PE = 79 N . 20 m
PE = 1,580 N.m
PE = 1,580 Joule
5. There is a bell at the top of a tower that is 45 m high. The bell weighs 190 N. The bell has ____________ energy. Calculate it.
Gravitational Potential Energy
PE = m.g.h
note: weight = m. g = 190 N
so put the weight directly to the equation below
PE = 190 N . 45 m
PE = 8,550 N.m
PE = 8,550 Joule
6. A roller coaster is at the top of a 72 m hill and weighs 966 N. The coaster (at this moment) has ____________ energy. Calculate it.
Gravitational Potential Energy
PE = m.g.h
note: weight = m. g = 966 N
so put the weight directly to the equation below
PE = 966 N . 72 m
PE = 69,552 N.m
PE = 69,552 Joule
7. What is the kinetic energy of a 3-kilogram ball that is rolling at 2 meters per second?
KE = 1/2 m v2
KE = 1/2 x 3 kg x (2 m/s)2
KE = 1/2 x 3 kg x 4 m2/s2
KE = 6 Joule
8. Object were lifted by a machine. One object had a mass of 2 kilograms if the Kinetic energy of the object was 1600 J. What was the velocity?
KE = 1/2 m v2
1,600 J = 1/2 x 2 kg x v2
v2 = EK /(1/2 x 2 kg)
v2 = 1,600 / 1
v = (1,600)1/2
v = 40 m/s
9. Determine the kinetic energy of a 1000-kg roller coaster car that is moving with a speed of 20.0 m/s.
KE = 1/2 m v2
KE = 1/2 x 1000 kg x (20 m/s)2
KE = 1/2 x 1000 kg x 400 m2/s2
KE = 200,000 Joule
