PHYSICS IN ENGLISH / PHYSICS 1 / MAY 22nd 2014.

THEORY (3 p)

(Use this sheet for your answer)

  1. A cylinder of height (20.00±0.05) cm and diameter (1.60±0.02) cm is made of copper. Knowing that its weight is (3.53±0.01) N, calculate the density of copper (1 p).
  1. Bernoulli’s law. Demonstration and brief explanation (2 p).

PROBLEMS (7 p)

PROBLEM 1 (4 p)

Three blocks A, B, C are hanging from a wheel of radius R= 10 cm by means of some thin threads as shown in the figure. The wheel can freely spin around its axle, which is light enough so that its mass can be neglected.
The massesof the wheel and the blocks are given below. Provided the threads are inextensible, calculate:
a)The acceleration of the blocks and the angular acceleration of the wheel (2 p).
b)The tension of the thread joining A and B (1 p).
c)If when t = 0 the system started to move from rest, find the elapsed time when blocks A and B have gone down 1 m (1 p).
Masses: wheel m = 0.320 kg; blocks:mA = 0.221 kg; mB = 0.342 kg; mC = 0.550 kg. /

PROBLEM 2 (3 p)

A cycle of Carnot uses 0.02 mole of nitrogen. The gas at 500 K is isothermally expanded from an initial volume of 250 cm3 up to reaching 1900 cm3 (step 1), then it is adiabatically expanded up to reaching 5000 cm3 (step 2). To round the cycle two compression steps follow: the gas is isothermally compressed (step 3) and finally it is adiabatically compressed (step 4).

a)Calculate the volume, pressure and temperature when step 3 is completed (1.5 p).

b)Calculate the work of this cycle (1 p).

c)Calculate the entropy variation for both isothermal steps in this cycle (1 p).