
Exercises and problems in Physics
September 1999 
New experimental problem:
M. 208. Measure the density of the material of a
tabletennis ball as accurately as you can. Give an error
estimation. (6 points)
New problems:
P. 3264. The value at "cement 600" shows that the
crosssectional area of 1 cm^{2} of a
concrete plate is capable to hold the weight of 600 kg. Using ten
times higher safety standard how high concrete tower can be made of
this kind of cement? The density of concrete is 2500 kg/m^{3}. (3 points)
P. 3265. The water runs into an insulated vessel
from two taps. The first tap gives 7 litres water per minute with
temperature 12 ^{o}C, while the other
gives 4 litres per minute with 60 ^{o}C. The cold water tap has been open for 8
minutes. How long should the hot water tap be open to get finally 36
^{o}C water in the vessel? (3 points)
P. 3266. In hail a piece of ice hits onto the roof
of a car with a speed of 6 m/s. How high does it bounce back at
most if 60%of its kinetic energy is lost in the collision? (3 points)
P. 3267. There are two identical open testtube in
a garden. One of them is in shadow, the other is placed on a very
sunny place. There is no wind at all. In which testtube is bigger the
energy of air
(4 points)
P. 3268. A glass of carbonated water is on the
table. Approximately how many CO_{2}
molecules are in a bubble of diameter 1 mm? (4 points)
P. 3269. A simple pendulum is hung on a
frictionless chart of mass M. The mass of the bob is m,
the length of the string is l. Fixing the chart the pendulum is
displaced a little bit and released. After measuring the period the
experiment is repeated not fixing the chart. How does the period of
the pendulum change? (4 points)
P. 3270. A satellite has a circular orbit of
radius r=2R around the Earth of radius
R=6370 km. In an instant it gets an extra velocity
directed to the centre of the Earth. The change of magnitude of its
linear momentum is equal the magnitude of momentum of the satellite
before.
a) Find the velocity of the satellite just after
the change of its momentum.
b) Find the minimum distance
of the satellite from the centre of the Earth after changing its
momentum.
c) What is its velocity at the closest point?
(5 points)
P. 3271. The diameter of the objective lens of a
Kepler telescope (of magnification 5) is 84 mm, its focal length
is 1 m, the diameter of its ocular (eyepiece) lens is 12 mm. Find
the maximum visual angle of this telescope to observe stars at the
same time. (5 points)
P. 3272. Suppose the rest heat of nuclear power
station in Paks of power 1800 MW and efficiency 30 % is using for
melting the ice cover of the frozen lake Balaton of thickness 10
cm. For how long would this quantity of ice melt? What surface should
be covered with solar cells constructing a solar power station having
a peak power identical with the permanent electric power of Paks? (The
intensity of the solar radiation on the surface of the Earth is
approximately 1 kW/m^{2}.) (4 points)
P. 3273. There is a very small hole on a heatable
furnace. In the vicinity of the furnace the temperature of air is 0
^{o}C, while the temperature inside is 57
^{o}C. In sufficient time the pressure in
the furnace becomes steady. Estimate this steady pressure. (6 points)
Send your solutions to the following address:
KöMaL Szerkesztőség (KöMaL feladatok),
Budapest Pf. 47. 1255, Hungary
or by email to: megoldas@komal.elte.hu.
Deadline: 15 October 1999
