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Five houses lettered A, B, C, D and E are built in a row next to each other. The houses are lined up in the order A, B, C, D and E. Each of the five houses have coloured roofs and chimneys. The roof and chimney of each house must be painted as follows:
1. The roof must be painted either green, red or yellow.
2. The chimney must be painted either white, black or red.
3. No house may have the chimney and the roof of the same colour .
4. No house may use any of the same colours that the next house on each side uses.
5. House E has a green roof.
6. House B has a red roof and a black chimney.
Which of the following is true?
At least two houses have black chimneys.
At least two houses have red roofs.
At least two houses have white chimneys.
At least two houses have green roofs.
Description : This is an interesting experiment to show the total internal reflection. We get the total reflection if the light enters to an optical less dense material and the incidence angle is big enough. The incidence angle at which the ray refracts exactly along the boundary line, is called the boundary angle of the total reflection. With the total reflection we can lead the light along the curved ways, as optic fibres or water jets.
As a car moves up a hill, there is a force of friction between the road and the tires rolling on the road. The maximum force of friction is equal to
a. the weight of the car times the coefficient of kinetic friction.
b. the normal force of the road times the coefficient of kinetic friction.
c. the normal force of the road times the coefficient of static friction.
e. the weight of the car times the coefficient of static friction.
Which of the following statements describes an electric generator?
A. A magnet is rotated through a coil of wire to produce an electric current.
B. Electric potential in a rotating coil of wire creates a permanent magnet.
C. An electrical current causes a coil of wire to rotate in a magnetic field.
D. Forces from a permanent magnet allow a coil of wire to rotate.
Question of the Day: You are in a boat on a perfectly calm lake. A floating log passes near. You grab the log and put it in the boat. During this process, does the level of the lake rise, fall, or stay the same?
Popoye and Bluto are playing tug-of-war. Popoye wins, pulling Bluto into the mud puddle. Why did Popoye win?
(a) Popoye exerted a greater horizontal component of force on the rope than Bluto exerted.
(b) The rope exerted a greater horizontal component of force on Bluto than it exerted on Popoye.
(c) Popoye exerted a greater horizontal component of force on the ground than Bluto exerted.
(d) All of the above.
A convex lens of glass is immersed in water. The power of the lens in water, as compared to its power in air, will
3. not change
4. diminish for red light and increase for violet light