
Exercises and problems in Physics
October 1999 
New experimental problem:
M. 209. Stand dominoes parallel to each other and at even
distances in such a way that pushing the first one makes all of them
tumble over. Investigate what the speed of the tumbling wave depends
on, and how. (6 points)
New problems:
P. 3274. The light of a searchlight placed at the top of a
26 meter high lighthouse standing on the seashore could first be seen
at 30 km from the shore, through the telescope of a ship. How high was
the telescope above the surface of the sea? (4 points)
P. 3275. How deep should a floating wooden log be submerged
into water so that the work done during the submerging is equal to the
minimum work necessary to lift the log out of the water? The density
of wood is k times smaller than that of water. Investigate the
case when k2. (4 points)
P. 3276. Make an estimate of the universal gas constant
using the following measurement data made on 100 ^{o}C steam.
p (Pa)  986 
9806  98066  (kg/m^{3})  0,00570  0,05705 
0,578 
(3 points)
P. 3277. Starting from the edge of a rock, Tarzan swings
towards another rock on a 18 m long liana. The bottom of his
trajectory is 3 metres lower than his starting point. Will the liana
support the jump of Tarzan, who weighs 900 N, if its maximum
tensile strength is 1200 N? (4 points)
P. 3278. Should two resistors of different resistances but
identical maximum power be connected in series or in parallel so that
their power is maximum together? (4 points)
P. 3279. One of the devices
used to measure gravitational acceleration is Whiting's plank
pendulum. Show that a ball in free fall starting together with the
plank from the rotational axis of the plank always hits the plank at
the same proportion of the length of the latter, regardless of the
actual length. What is this proportion? (4 points)
P. 3280. Should the volume of air saturated with steam be
decreased or increased in order to condense some of the water from the
air? (4 points)
P. 3281. Determine the radius
of curvature at the topmost point of the trajectory described by a
point of a hoop rolling without sliding on a slope. (5 points)
P. 3282. A circular conductor of radius R is
electrically charged with charge Q. How does the electric field
strength change along the straight line crossing the centre of the
circle and perpendicular to the plane of the circle? Where does it
reach its maximum value? (5 points)
P. 3283. The suspension springs of all the wheels of a car
are identical. How much does the body of the car (considered as rigid)
rise above the wheels when the car is parked on a 8 cm high kerb
with its right front wheel? How does the result change when the car is
parked with both its right wheels on the kerb? Does the result depend
on the number and the position of the persons sitting in the car? (6
points)
