WORK(W)The work done by a constant force acting in the same direction as the displacement.W = Fs (N-m or Joules)The work done by a constant force acting at an angle to the displacement. W = Fscos

WORK(W)

WORK(W)

WORK(W)Example 1.

WORK(W) & KINETIC ENERGY(K)ConsiderNewtons 2nd Law of MotionKinematics

WORK(W) & KINETIC ENERGY(K)

WORK(W) & KINETIC ENERGY(K)

ConsiderKinetic Energy(K) - energy due to motion.So, WORK-ENERGY THEOREMIf v1 = 0Then K1 = 0, soKinetic energy is also the amount of work needed to bring a body at rest to motion with speed v .orWORK(W) & KINETIC ENERGY(K)

Example 2.A baseball leaves a pitchers hand at a speed of 32 m/s. The mass of the baseball is 0.145kg. You can ignore air resistance. How much work has the pitcher done on the ball by throwing it?Example 3.Consider Example 1, the given and computed quantities. Suppose the initial speed v1 is 2 m/s, what is the speed of the sled after it moves 20 m?WORK(W) & KINETIC ENERGY(K)

Example 4.WORK(W) DONE BY A VARYING FORCE(F)

Example 5.WORK(W) DONE BY A VARYING FORCE(F)

POWER(P)- The rate of doing work.Instantaneous PowerAverage Power

POWER(P)Example 6.When its 75-kW (100-hp) engine is generating full power a small single-engine airplane with mass 700 kg gains altitude at a rate of 2.5 m/s. What fraction of the engie power is being used to make the airplane climb? (The remainder is used to overcome the effects of air resistance and of ineffeciencies in the propeller and engine.)

WORK(W) & GRAVITATIONAL POTENTIAL ENERGY(Ug)Since weight w & displacement s have the same direction, work done by the weight is positive. So it has to be: Gravitational PotentialEnergy (Ug)So,orConsider a body moving downward

WORK(W) & GRAVITATIONAL POTENTIAL ENERGY(Ug)Since weight w & displacement s have the opposite direction, work done by the weight is negative. So, still, it has to be: Gravitational PotentialEnergy (Ug)So,orConsider a body moving upward

WORK(W) & GRAVITATIONAL POTENTIAL ENERGY(Ug)Consider a body moving in a curved pathStill,orFrom,Since,

WORK(W) & ELASTIC POTENTIAL ENERGY(Uel)Recall:Fapplied = kxWork done on the spring by Fapplied is:

WORK(W) & ELASTIC POTENTIAL ENERGY(Uel)Recall N3LM :Fapplied = kxFspringN3LM:So, Work done by the spring:Elastic PotentialEnergy (Uel)or,

LAW OF CONSERVATION OF ENERGYRecall WORK-ENERGY THEOREM:orIf Wother = 0, the Total Mechanical Energy(U + K) of a body at any point is constant!

LAW OF CONSERVATION OF ENERGYExample 7.A 2.00 kg block is pushed against a spring with negligible mass and force constant k = 400 N/m, compressing it 0.220m. When the block is released, it moves along a frictionless, horizontal surface and then up a frictionless incline with slope 37o. a) What is the speed of the block as it slides along the horizontal surface after having left the spring? b) How far does the block travel up the incline before starting to slide back down?

LAW OF CONSERVATION OF ENERGYExample 8.In a truck-loading station at a post office, a small 0.200-kg package is released from rest at point A on a track that is one-quarter of a circle with radius 1.60 m, as shown below. The size of the package is much less than 1.60 m, so the package can be treated as a particle. It slides down the track and reaches point B with a speed of 4.80 m/s. From point B, it slides on a level surface a distance of 3.00 m to point C, where it comes to rest. a) What is the coefficient of kinetic friction on the horizontal surface? b) How much work is done on the package by friction as it slides down the circular arc from A to B?