
Problems with sign 'P'
Deadline expired on 11 October 2005. 
P. 3813. How can a gold leaf electroscope be charged a) negatively, b) positively by using a plastic rod, which was rubbed by a piece of fur?
(3 pont)
statistics
P. 3814. Given eight 600 resistors, how should they be connected if the equivalent resistance is 750 ?
(3 pont)
statistics
P. 3815. A car travels at a speed of 12 km/h towards south for five minutes, then it turns toward east and moves at a speed of 25 m/s for 3 minutes, and finally it changes its velocity to 108 km/h and travels toward northeast for two minutes. Calculate the length of its displacement and the average speed.
(3 pont)
statistics
P. 3816. Two bodies collide. Before the collision the linear momentum of one of them was , and the other was at rest. After the collision can the linear momentum of the second body (which was initially at rest) be ? If yes, at which case?
(4 pont)
statistics
P. 3817. A uniform cylinder is placed to a slope inclined at an angle of . The symmetry axis of the cylinder is horizontal. The coefficient of kinetic friction is 0.2. Find the acceleration of the cylinder.
(5 pont)
statistics
P. 3818. Can it ever happen that the total eclipse of the Sun is followed by a total eclipse of the Moon (or maybe in reversed order)?
(3 pont)
statistics
P. 3819. The density of a uniform rod with crosssection A is , its specific heat capacity is c and the coefficient of its linear expansion is . Calculate the amount of heat that should be added in order to increase the length of the rod by l.
(3 pont)
statistics
P. 3820. Edison's first incandescent lamps were made of carbonized fibres of plants. Why was it important to connect a resistor in series?
(4 pont)
statistics
P. 3821. Find the least size of that mirror in which a 1.7m tall person can see himself from top to toe, if his head is 2 m away from the plane of the mirror, which makes a 30^{o} angle with the vertical.
(5 pont)
statistics
P. 3822. The DLP chip (Digital Light Processor), developed by Texas Instruments, is a new display solution used in modern projectors. Peter heard that the chip contains millions of hingemounted microscopic mirrors, and all of them can be tilted (separately) into two positions (even 5000 times in a second) reflecting or not reflecting light onto the screen. He lighted the rectangular chip of sides 17 mm and 9.5 mm nearly perpendicularly by a laser beam of wavelength 633 nm. He observed that the reflected laser light formed a diffraction pattern of a grid of squares with 2.4 cm long sides on a screen 50 cm from the chip. Using these data find the length of the sides and the number of the micromirrors in the chip.
(4 pont)
statistics
P. 3823. Why don't you observe an apple 6 m away from you darker than another one 2 m from you? Isn't it true that your eyes receive less light reflected from the apple further away?
(4 pont)
statistics