Balkan physics competition

You have a plastic and an aluminum plate. You place two ice cubes at the same time on each. Is it going to melt on aluminum or plastic faster?

• On the plastic, because it feels hotter than the aluminum

• Will melt at the same rate because they are in the same enviroment

• Will melt faster on the aluminum because of higher thermal conductivity

• Will be faster on plastic because of higher thermal conductivity

A massless rod, from which the loads of weights W and 2W are suspended, is in equilibrium, as shown in the figure.

What is the ratio of the tension one to tension two

(The length of each section of the rod is equal.)

• 2

• 5/3

• 0.6

• 0.5

• 5

• 2

• 4

• 3

The system composed of objects K and L, as shown in the figure, moves with a constant speed. What is the ratio of

the greatest possible value of the mass of object L to the least possible value of its mass?

(Take g=10 N/kg; sin37°=0,6; cos37°=0,8)

• 1/2

• 4/3

• 3/2

• 2

Which one below is not correct about temperature?

• At absolute zero temperature kinetic energy becomes zero

• Temperature means average kinetic energy

• Zero Kelvin is the smallest temperature

• Temperature is the total kinetic energy of the system

An object is attached by a string to the ceiling of a vehicle. When the vehicle moves with an acceleration of a, the string makes an angle of 37° with the vertical axis.

What is the acceleration of the vehicle in terms of g? (Take sin 37°=0.6; cos 37°=0.8)

• 4/3

• 1/3

• 3/4

• 1

A lead bullet moving at v = 200 m/s strikes and embeds into a wooden wall. By how much celsius degrees does its temperature increase? Suppose 70% of heat produced by the impact is absorbed by the bullet. (clead ≈ 126 J/kg⋅°C)

• 111

• 150

• 32

• 158

If the resistance of X is 2 Ω.

What is the Potential difference V for battery (all

conductors made from same material)?

• 5

• 7

• 15

• 10

For the network shown in the figure the equivalent resistance between points K and L is R1 and equivalent

resistance between K an M is R2. What is the ratio of R1/R2?

• 2/5

• 4/5

• 5/4

• 3/5

In which one below you cannot produce current?

• When a coil rotates in magnetic field

• When a wire moves in a magnetic field

• When a coil moves in and out of a magnetic field

• When you place a wire in a magnetic field