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Knight Ch 11 - work-notes

# Knight Ch 11 - work-notes - Work Chapter 11 Energy...

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W __ 0The environment does work on the system and the system’s energy increases. W __ 0The system does work on the environment and the system’s energy decreases. Energy transformations within the system ______ change the value of E sys . Systems are typically not ___________ from their environment and therefore exchange energy with the environment. The mechanical transfer of energy is called ________. Work - Chapter 11 Positive, Negative and Zero Work Keep track of whether work is positive, negative, or zero. Positive work _____________ speed. Negative work _____________ speed. Zero work has _____________ on speed. Apple Falls W __ 0 Apple ______ W ____ 0 Apple __________ r r mg mg Work dt dv m ma F s s s = = ds dv mv dt ds ds dv m dt dv m s s s s = = ds dv mv F s s s = s ds F = = f i f i v v s s s s s dv mv ds F 2 i 2 f v v 2 s s s s mv 2 1 mv 2 1 mv 2 1 ds F f i f i = = ___________ Work 2 i 2 f v v 2 s s s s mv 2 1 mv 2 1 mv 2 1 ds F f i f i = = You will also notice that this equation also reads that ___________. To change a particles energy, a ___________ must be applied to the particle as it undergoes a displacement. v i v f Σ F x K mv 2 1 mv 2 1 ds F W 2 i 2 f s s s f i = = =

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Work In the simplest case, when the force F and the displacement r are ____________ , this definition of the work is given by W = F [W] = ______ = J = joule (J) named for James Prescott Joule In general, work is the component of the the force parallel to the displacement multiplied by the displacement. So, only forces in the direction of _______________ count. r F ___________ Work W = F r _______ F = 50.0N r = 10.0m θ = 30.0 0 W = 50.0N (10.0m) ____________ = 430 Nm = 430 J Example: Hannah’s grandma pulls a wagon with a force of 50.0 N. The handle makes a 30.0 o angle with the ground. The wagon moves 10.0m. Calculate the work. Note: the ___________ force does no work since it is _________________ to the displacement Work is the component of the the force parallel to the displacement multiplied by the displacement. Accelerate the Car To accelerate a car from rest to a speed v requires the work W 1 . The work needed to accelerate the car from v to 2v is W 2 . Using the work – energy theorem: W net = _________________ Let’s calculate W 1 v i = ___, v f = _____ W 1 = ______________________________ Calculating W 2 v i = _____, v f = ________ W 2 = _____________________ W 2 = ____W 1 Kinetic Energy a) K f = ___________ K f = W net + _____ K f = ____________ = 4500 N (100 m) = 4.5 x 10 5 J b) _________ = F x = 4.5 x 10 5 J v = 25.4 m/s m J x v ) 10 5 . 4 ( 2 5 = A 1400 kg boat has a forward force of 4500 N applied. The boat starts from rest and travels 100 m. What is the final kinetic energy and the velocity of the boat?
Friction does _____ work on the car.

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