2 The HOT, BURNING News TODAY: Mechanical Energy and its types: DISCOVEREDWhat is meant by Conservation of Mechanical Energy: ANSWEREDTHINGS TO REMEMBER when solving conservation of Energy problemsFormulas to be IMPLANTED on mind and EXAMPLES of Energy TransfersProblem SOLVED
3 Mechanical Energy and its types: DISCOVERED Mechanical Energy is the sum of KINETIC and POTENTIAL ENERGY.3 TYPES:Kinetic Energy a.k.a. KEGravitational Potential Energy a.k.a PEgElastic Potential Energy a.k.a. PEs
4 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.
5 THINGS TO REMEMBER when solving conservation of Energy problems 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.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.Finally, if there is no friction, find the initial and final total energies and set them equal
6 Formulas to be IMPLANTED on mind and EXAMPLES of Energy Transfers KEi + PEi = KEf + PEf PE = mgh KE = ½ mv2
7 Formulas to be IMPLANTED on mind and EXAMPLES of Energy Transfers KEi + PEi = KEf + PEfPE = mghKE = ½ mv2
8 Formulas to be IMPLANTED on mind and EXAMPLES of Energy Transfers KEi + PEi = KEf + PEfPE = mghKE = ½ mv2
9 Formulas to be IMPLANTED on mind and EXAMPLES of Energy Transfers KEi + PEi = KEf + PEfPE = mghKE = ½ mv2
10 Problem SOLVEDProblem: 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?
11 Problem SOLVED Given: m = 15.0 kg Unknowns: a. Kef b.Vf g = 9.80 m/s2 Basic Equations: KEi + PEi = KEf + PEfGiven: m = 15.0 kgg = 9.80 m/s2h = 8.00 mKEi = 0PEf = 0Solution:KEi + PEi = KEf + PEf0 + mgh = KEf + 0KEf = mgh = (15.0 kg) (9.80 m/s2) (8.00 m) = 1.18 x 10^3 J
12 Problem SOLVEDb. 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
14 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?
15 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?