Clarification……. v = d t Sometimes the question will use the word VELOCITY instead of speed.
A place to look for a missing numberA place to look for a missing number Determine what the units should beDetermine what the units should be
Practice Problem #1 A person pushes a large box across a level floor by applying a horizontal force of 200 N. If the person pushes the box a distance of 5 meters in 10 seconds, how much work does the person do on the box? A 2000 joules B 1000 joules C 400 joules D 100 joules force of 200 N distance of 5 meters 10 seconds work Work =force x distance W=Fd W=Fd W= (200N)(5m) = 1000 joules *notice 10 seconds was not needed
Practice Problem #2 In this circuit, how much current flows through the light bulb? A 0.75 amp B 1.50 amps C 2.0 amps D 3.0 amps current Current = voltage = V resistance R Current = 1.5 volts = 0.75 amp 2.0 ohms
Let’s Practice…….. *work on problems #1-5 on your worksheet
Two steppers….. Two steppers….. Problems that involve the use of two formulasProblems that involve the use of two formulas The two formulas have a common termThe two formulas have a common term
Two Stepper #1 Two Stepper #1 What is the net force acting on a 90.0 kg race- car driver while the race car is accelerating from 0 to 44.7 m/s in 4.50 s? What is the net force acting on a 90.0 kg race- car driver while the race car is accelerating from 0 to 44.7 m/s in 4.50 s? A 9.8 N A 9.8 N B 20 N B 20 N C 201 N C 201 N D 894 N D 894 N force force F=ma m= 90.0 kg 90.0 kg a= ____ F= ? We need to know “a”, to get our answer. Let’s find another equation. a=v f -v i t t a=44.7m/s-0m/s 4.50 s 4.50 s 9.9 m/s 2 D 894 N 0 to 44.7 m/s in 4.50 s?
Two stepper #2……………… Starting from rest at the center of a skating rink, two skaters push off from each other over a time period of 1.2 s. What is the force of push by the smaller skater? A 16 N B 32 N C 88 N D 100 N force F=ma smaller m=40 kg a=_____..another equation a=v f -v i t t rest 1.2 s a= 3.0 m/s-0m/s 1.2 s 1.2 s 2.5 m/s 2 D 100 N
F = m x a and W = F x d W= F x d and P = W W= F x d and P = W t Two steppers: other common combinations
Conceptual Questions Energy: the ability to cause change The Sun is the #1 source of energy for Earth
Energy can be transformed from one form to another. UV
Energy can be transformed from one form to another. Photosynthesis
Which of the following is an example of solar energy being converted into chemical energy? a.Plants producing sugar during the day b.Water evaporating and condensing in the water cycle water cycle c.The sun unevenly heating Earths surface d.Lava erupting from volcanoes for many days
The Law of Conservation of Energy: The total energy of a closed system is constant.
An inventor claims to have created an internal combustion engine that converts 100 kJ of chemical energy from diesel fuel to 140 kJ of mechanical energy. This claim violates the law of conservation of -- a.momentum b.inertia c.energy d.mass
A helpful hint…………….. Gravitational potential energy = Potential Energy
If the energy of a closed system changes, then you will observe changes in the system Energy of a System Working W=F x d See a change in motionSee a change in motion Heating Q=mc t Feel a temperature changeFeel a temperature change Radiating V = f Hear soundHear sound See lightSee light
Heating…… Convection!!!!!!Convection!!!!!! The answer any time the words: air, liquid, water or fluid are used.The answer any time the words: air, liquid, water or fluid are used. When in doubt guess convection.When in doubt guess convection.
When a DVD is read, laser light touches the DVD surface and is then measured at location A. What allows light to return to location A after striking the DVD surface? a.Conductionc. Magnification b.Refractiond. Reflection
Refraction: bending of wave when it enters a new substance (medium)Refraction: bending of wave when it enters a new substance (medium) Wave behavior…………….. air water
When trying to spear a fish in water, a person needs to take into account the way light bends as it moves from water into air. The bending of light as it passes from one medium into another is known as -- a.reflectionc.diffraction b.refractiond.polarization
Resonance: one vibrating object causing another object to start vibrating (musical instruments)Resonance: one vibrating object causing another object to start vibrating (musical instruments) Sound….requires vibrations
A guitar player is seated next to a piano. The piano player strikes an E key on the piano. The guitarist reports that this causes the E string on his guitar to vibrate. What is the name of this phenomenon? a.Polarizationc.Reflection b.Resonanced.Diffraction
Diffraction: waves spreading out when they pass through an openingDiffraction: waves spreading out when they pass through an opening Wave behavior………………. D
The diagram below shows waves approaching a barrier. Which pattern will form after the waves pass through the opening in the barrier? A B C D
Don’t forget………. Speed of light and soundSpeed of light and sound