RK Patrol
The HOT, BURNING News
TODAY:
Mechanical Energy and its types: DISCOVERED
What is meant by Conservation of Mechanical Energy:
ANSWERED
THINGS TO REMEMBER when solving conservation of
Energy problems
Formulas to be IMPLANTED on mind and EXAMPLES of
Energy Transfers
Problem SOLVED
Mechanical Energy and its types:
DISCOVERED
Mechanical Energy is the sum of KINETIC and POTENTIAL
ENERGY.
3 TYPES:
1. Kinetic Energy a.k.a. KE
2. Gravitational Potential Energy a.k.a PEg
3. Elastic Potential Energy a.k.a. PEs
What is meant by Conservation of
Mechanical Energy: ANSWERED
In a closed system, nothing leaves and
nothing enters. Therefore, in a closed system,
total mechanical energy is conserved.
An example of a mechanical system: A
satellite is orbiting the Earth only influenced by
the conservative gravitational force and the
mechanical energy is therefore conserved.
THINGS TO REMEMBER when solving
conservation of Energy problems
1. Carefully identify the system. Make sure it is closed; no objects can enter
it or leave it. It must also be isolated; no external force can act on any
object in the system. Thus, no work can be done on or by objects outside
the system.
2. Is friction present? If it is, then the sum of kinetic and potential energy
will not be constant. But, the sum of kinetic energy, potential energy and
the work done against friction will be constant.
3. Finally, if there is no friction, find the initial and final total energies and
set them equal
Formulas to be IMPLANTED on mind
and EXAMPLES of Energy Transfers
KEi + PEi =
KEf + PEf
PE = mgh
KE = ½ mv2
Formulas to be IMPLANTED on mind and
EXAMPLES of Energy Transfers
KEi + PEi = KEf
+ PEf
PE = mgh
KE = ½ mv2
Formulas to be IMPLANTED on mind and
EXAMPLES of Energy Transfers
KEi + PEi = KEf +
PEf
PE = mgh
KE = ½ mv2
Formulas to be IMPLANTED on mind and
EXAMPLES of Energy Transfers
KEi + PEi =
KEf + PEf
PE = mgh
KE = ½ mv2
Problem SOLVED
Problem:
A large chunk of ice with mass 15.0 kg falls from a roof 8.00 m above e
the ground a. Find the kinetic energy of the ice when it reaches the
ground b. What is the speed of the ice when it reaches the ground? c.
Is the answer the same as you would determine by solving as a constant
acceleration problem?
Problem SOLVED
Given: m = 15.0 kg
g = 9.80 m/s2
h = 8.00 m
KEi = 0
PEf = 0
Unknowns: a. Kef
b.Vf
Basic Equations: KEi +
PEi = KEf + PEf
Solution:
a. KEi + PEi = KEf + PEf
0 + mgh = KEf + 0
KEf = mgh = (15.0 kg) (9.80 m/s2)
(8.00 m) = 1.18 x 10^3 J
Problem SOLVED
b. KEf = ½ mvf2
vf2 = 2KEf = 2(1.18 x 10^3 J) =157 m2/s2
m
15.0 kg
vf = 12.5 m/s
c. yes
THE END
Questions to Answer
• I. IDENTIFICATION
• 1. What is mechanical energy?
• 2 – 4. Give the 3 types of Mechanical
energy and their corresponding examples.
(0.5 point each number)
• 5. What is meant by Conservation of
Mechanical Energy?
• 6. A mechanical system has been mentioned earlier
and in connection to that, cite an example of it.
• 7-9. Identify the formulas needed to be implanted
on mind with regards to this topic.
• 10. What formula would perfectly suit to this
problem and how is it derived?
•
Bill throws a 10 g ball straight down from a
height of 2.0m. The ball strikes the floor at a speed
of 7.5 m/s. What was the initial speed of the ball?