Exercises and problems in Physics October 2002
 Experimental problem 
M. 236. In the vinification process new wine
is drawn from an upper barrel into a lower one through a rubber
hose. Model this process with water. Examine the dependence of the
water stream velocity on the level difference and on the length of the
hose. (6 points)
 Theoretical problemsIt is allowed to
send solutions for any number of problems, but final scores of
students of grades 912 are computed from the 5 best score in each
month. Final scores of students of grades 18 are computed from the 3
best scores in each month. 
P. 3551. A crane driven by a toy DC
electromotor is lifting a load of a mass of 200 g with
0.2 m/s velocity. What is the power of the crane's electromotor
if 10% of the overall power goes against the friction? How much is the
current drain of the 9 V electromotor if its efficiency is 80%?
(4 points)
P. 3552. We try to measure the depth of
a well on the basis of the delay of the splash of a stone we have
dropped in. What is the error of the depth measurement if the error of
our time measurement is p %? Neglect the aerodynamic drag and
the time of sound propagation. When is it allowable to discard these
data? (4 points)
P. 3553. Add forces of magnitude
F and kF including an \(\displaystyle \alpha\) angle with each other (k1). At what angle ,
the angle of the resultant force and component kF, will be the
greatest? What is this angle? (5 points)
P. 3554. We release a solid ball and a
cylinder from the top of a slope at the same time. Can they reach the
bottom at the same time as well? (4 points)
P. 3555. We stand in front of a
wall. Between us and the wall, at the height of our ears, there is a
whistle blowing, at a frequency of 600 Hz. How fast must the
whistle go towards the wall so that we can hear 3 beats a second? (4
points)
P. 3556. Inside the airgap of a
toroidal coil the magnetic field has a circular cross section and it
can be considered homogeneous. If charged particles are coming in a
radial direction perpendicular to the magnetic field lines, do the
slower or the faster ones leave the magnetic field in a shorter time?
(5 points)
P. 3557. A light beam is falling on the
hypotenuse of a rectangular symmetric glass prism from the air. Choose
the \(\displaystyle \alpha\)
angle of incidence so that total reflection will occur at both
opposing sides (n=1.5). a) Determine the angle
included by the beams incoming and leaving the
prism. b) What maximum value can we choose for angle , so that
total reflections still occur? (5 points)
P. 3558. In an atomic reactor the slow,
thermal neutrons cause atomic fissions with a greater probability than
the faster ones. Therefore, the neutrons emerging from fission
processes must be decelerated (moderated) with deuterium oxide or
graphite. Determine what fraction of its energy does a neutron lose in
a straight elastic collision with a ^{2}_{1}H and a
\(\displaystyle {}^{12}_{\phantom{1}6}\rm C\) atomic nucleus. (4 points)
P. 3559. Estimate what percentage of
the area of Hungary has to be covered with modern (50% efficiency)
solar panels if the current electric power need of the country
(7 GW on average) is to be supplied by them. (5 points)
P. 3560. There is a 1 m long
horizontal rod. One of its ends is fixed and on the other a body of a
mass of 1 kg is hung causing a 1 cm deflection. Estimate the
force F under which the same, vertically placed rod
collapses. (Hint: the elastic energy of a bent rod is proportional to
its length and inversely proportional to the square of the radius of
curvature.) (6 points)
Send your solutions to the following address:
KöMaL Szerkesztőség (KöMaL feladatok), Budapest 112,
Pf. 32. 1518, Hungary or by email to:
Deadline: 11 November 2002
