HESI A2
HESI Exams Quizlet Physics
1. An electromagnet is holding a 1,500-kg car at a height of 25 m above the ground. The magnet then experiences a power outage, and the car falls to the ground. Which of the following is false?
- A. The car had a potential energy of 367.5 kJ.
- B. 367.5 kJ of potential energy is converted to kinetic energy.
- C. The car retains potential energy of 367.5 kJ when it hits the ground.
- D. The car’s potential energy converts to kinetic energy and then to sound energy.
Correct answer: C
Rationale: When the car falls to the ground, its potential energy is converted to kinetic energy as it accelerates downwards. Upon impact with the ground, the car's kinetic energy is dissipated in various forms, such as sound energy, heat, and deformation energy. Therefore, the car does not retain its initial potential energy of 367.5 kJ when it hits the ground. Choice A is true because the potential energy of the car can be calculated as mgh = 1500 kg * 9.8 m/s^2 * 25 m = 367,500 J = 367.5 kJ. Choice B is true because as the car falls, its potential energy is converted to kinetic energy. Choice D is true as the kinetic energy is eventually dissipated into other forms upon impact.
2. When a car is driven for a long time, the pressure of air in the tires increases. This is best explained by which of the following gas laws?
- A. Boyle's law
- B. Charles' law
- C. Gay-Lussac's law
- D. Dalton's law
Correct answer: C
Rationale: Gay-Lussac's law, also known as the law of pressure-temperature, states that the pressure of a gas is directly proportional to its absolute temperature when the volume is constant. As a car is driven for a long time, the tires heat up due to friction and increased air pressure inside the tires. This results in an increase in temperature, causing the pressure of the air inside the tires to increase according to Gay-Lussac's law. Choices A, B, and D are incorrect. Boyle's law relates pressure and volume, Charles' law relates volume and temperature, and Dalton's law deals with the partial pressures of gases in a mixture.
3. Bernoulli's principle for an incompressible, inviscid fluid in steady flow states that the mechanical energy, consisting of:
- A. Pressure (P) only, remains constant along a streamline.
- B. Velocity (v) only, remains constant along a streamline.
- C. P + ½ρv² (total mechanical energy), remains constant along a streamline
- D. Density (ρ) only, remains constant along a streamline.
Correct answer: C
Rationale: Bernoulli's principle states that the sum of pressure energy (P), kinetic energy per unit volume (½ρv²), and potential energy per unit volume remains constant along a streamline in an incompressible, inviscid fluid. This means the total mechanical energy of the fluid is conserved, making Choice C the correct answer. Choices A, B, and D are incorrect because Bernoulli's principle involves the conservation of the total mechanical energy, not just pressure, velocity, or density alone.
4. A constant force is exerted on a stationary object. In this scenario, work is:
- A. Performed
- B. Not performed
- C. Partially performed
- D. Inconclusive without further information
Correct answer: B
Rationale: Work is only done when a force causes displacement. Since the object is stationary, no displacement occurs, and therefore, no work is performed. Choice A is incorrect because work requires both force and displacement. Choice C is incorrect as there is no partial work - work is either done or not done. Choice D is incorrect as the scenario provided is clear - the object is stationary, so no work is being performed.
5. A 0-kg block on a table is given a push so that it slides along the table. If the block is accelerated at 6 m/s2, what was the force applied to the block?
- A. 0 N
- B. 3 N
- C. 6 N
- D. The answer cannot be determined from the information given.
Correct answer: A
Rationale: According to Newton's second law of motion, F=ma. Since the block has a mass of 0 kg, the force applied must be 0 N, as no force is needed to move an object with zero mass.
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