Transcript Class Notes 11-30 ps - elyceum-beta

Class Notes 11-30 ps
Hand back Papers
Grades
Solving Problems through calculations
Steps to solve problems
1) Identify GIVENS, and what is WANTED
2) DRAW pictures and LABEL values
3) IDENTIFY the EQUATION that connects
givens and what is wanted
4) CONVERT units, if needed
5) PLUG in values, including constants
6) Solve, DO the MATH
7) CHECK answer, units
Watch out for the hidden
values!
Goal of session
• Answer the questions placed around the room
• Students may precede in any order
• SHOW WORK!! For each problem state:
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Givens
What is wanted
Equation
Conversions done
Values plugged into equation
Answer with units
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F = ma
GPE = mgh
p=mv
P= W/t
W = Fd
a = (vf -vi)/t
KE = ½mv2
MA = Fo / fi
Remember…
That I used 9.8 as the
acceleration due to gravity and a
rounded some of the answers
Question #1
• A force of 6.2 x 105 N is needed to blast off
a 5.0 x 103 kg rocket from rest. What is
the rocket’s average acceleration?
• Answer: 124 m/s2
Question #2
• How much does a 59.0 kg woman weigh
on Earth?
• Answer 578.2 N
Question #3
• A coin falls from rest from the balcony of a
building. If it takes 2.7 s for it to hit the
ground, what is the final velocity of the
coin?
• Answer : 26.5 m/s
Question #4
• An object has a kinetic energy of 810 J
after falling a certain distance. If the
mass of the object is 20 kg, what is the
speed of the object at this time?
• Answer: 9 m/s
Question #5
• The brakes on a car exert a frictional force
of 6000N in getting the car to stop. If the
work done by the brakes is 120,000 J in
coming to a stop, how many meters did
the car travel after the driver applied the
brakes?
• Answer: 20 m
Question #6
• An object weighing 75 N is dropped from
the top of a building and falls a distance of
28 m to the ground. How much work
does gravity do on the object from the time
it is dropped to the time it hits the ground?
• Answer: 2100 J
Question #7
• A weightlifter presses a 400 N weight 0.5
m over his head in 2 seconds. What is
the power of the weightlifter?
• Answer: 100 W
Question #8
• Calculate the gravitational potential energy
relative to the ground when an 82 kg
person climbs to the top of a 2.0 m
stepladder.
• Answer: 1607 J
Question #9
• A crane has a mechanical advantage of
27. An input force of 8650 N is used by
the crane to lift a pile of steel girders.
What is the weight of the girders?
• Answer: 233550 N
Question #11
• A commercial plane travels at a velocity of
234 m/s. The plane has 253 people
seated onboard. If the average person
on the plane has a mass of 68,000 g, what
is the momentum of the passengers on the
plane?
• Answer 4,026,000 kg m/s
Question #12
• A school bus can accelerate from a
complete stop at 1.3 m/s2. How long will
it take the bus to reach a velocity of 12.1
m/s?
• Answer: 9.31 s
Question #13
• A cat sits on top of a fence that is 2.0 m
high. The cat has a GPE of 88.9 kJ .
What is the mass of the cat?
• Answer: 1,742,000 J
Old Homework
• 858,859 111-125?
• Homework to be handed in tomorrow!
– Page 858: 101-103, 106-108
– Page 857:96-98
– Page 852: 6-9
Scientific Notation
• A way to write very large or very small
• Convert number to a specific form (set-up)
A number between 1-10 x 10 to an exponent
Positive exponents for large #
Negative exponents for small #
Examples
• 2,407,000 =
Examples
• 0.000305=
Try
• 6,907,800,000
• Answer
• 6.9078 x109
Try
• 0.000 000 080 07
• Answer:
• 8.007 x 10-8
Conservation of energy equation
• GPEi + KEi = GPEf = KEf
• The total amount of energy is constant, but
the amount in each form may change
• If there is a gain in KE, there is a loss in
GPE
Cliff Diving