# Ejercicios de calor y electricidad

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Physics (H&E) Final Exam
Prep Questions

Pressure

1. An 85-kg athlete does a single-hand handstand. If the area of the hand in contact with the floor is 125 cm2, what is the pressure exerted on the floor?

Fluids

2. A hydraulic jack in garage has two circular pistons: a small one with radius of 2.00 cm and a large one with a radius of 15.0 cm. If this lift is designedto raise a 3000-kg car, what minimum force must be applied to the small piston?

3. A aluminum cube 0.22 m on a side is completely submerged in (fresh) water. What is the buoyant force on it? What is its apparent weight when completely submerged? (Note: density of aluminum = 2.7 x 103 kg/m3)

4. An ideal fluid is moving at 3.0 m/s in a section of a pipe of radius 0.20 m. If theradius in another section is 0.35 m, what is the flow speed there? Imagine the ideal fluid to be water, ¿What is the pressure difference between the sections?

Heat

5. A 0.100-kg piece of aluminum at 90º C is immersed in 1.00 kg of water at 20º C. Assuming no heat losses to the surroundings, what is the temperature of the metal and water when they reach thermal equilibrium? (Note: thespecific heat of Al is 0.220 [pic] )

6. Fifteen (15) kilocalories would raise the temperature of three (3) liters (L) of water how many degrees Celsius?

7. How much heat is required to raise the temperature of 0.20 kg of (liquid) water from 15° C to 45° C?

Thermodynamics

8. For which thermodynamic process does ΔU = 0? W = 0? Q = 0? W = PΔV?

9. During an isobaricexpansion of an ideal gas, volume changes from 1.3 L to 3.8 L at a constant pressure of 2.0 atm. What is the work (in J) done on or by the gas?

Sound

10. Find the sound intensity level (in dB) for a sound with an intensity of 1.6 x 10-7 W/m2. What is the intensity (in W/m2) for sound level of 122 dB?

11. What is the frequency heard by a person driving 50 km/hr directly away froma (stationary) factory whistle (f = 800 Hz) if the air temperature is 30º C?

12. One noise is 63 dB louder than another noise. How many times larger is the intensity of one noise than the other?

Electric potential

13. A proton is moved from the negative to the positive plate of a parallel plate system. The plates are 1.50 cm apart and the electric field is uniform with amagnitude of 1500 N/C. What is the electrical potential energy gain of the proton?

Simple harmonic motion

14. A particle in simple harmonic motion (SHM) has a frequency of 40 Hz. Calculate the period of oscillation.

15. When a mass m oscillates on a spring, its period is observed to be T. A mass of 2m is now placed on the spring and it again obeys simple harmonic motion (SHM). Whatis the period now (with the new mass)?

Latent heat & phase changes

16. For lead (Pb), the latent heat of fusion (Lf) is 5.9 kcal/kg, the latent heat of vaporization (Lv) is 207 kcal/kg, and its melting point is 328° C. How much heat is required to melt 50 g of Pb (solid) initially at 23° C to Pb (liquid) at 328° C? (Note: The specific heat of Pb (s) is 0.031 kcal/ (kg·°C).)Ideal gas law

17. In a rigid container, the original temperature of an ideal gas is 20° C when the pressure is 1.0 atm. If the pressure is doubled, what is the new temperature (in °C)?
18. What is the number of moles in 2.0 L of oxygen gas at a pressure of 3.0 atm and a temperature of 100° C?

Electric force

19. What is the magnitude of the repulsive electric force betweentwo protons in a nucleus? (Note: Take the distance between the center of the nuclear protons to be 3.0 x 10-15 m.)

20. An electron and a proton are separated by a distance of 1 m. What happens to the size of the force on the proton if the electron is moved 0.5 m closer to the proton?

Hooke’s law

21. When a 0.50-kg mass is suspended from a spring, the spring stretches a...