HESI A2
HESI A2 Physics Quizlet
1. When a small object floats on the surface of a liquid, the surface tension creates a:
- A. Buoyant force acting upwards
- B. Pressure difference causing sinking
- C. Drag force opposing motion
- D. Restoring force towards equilibrium
Correct answer: D
Rationale: Surface tension creates a restoring force that holds the object on the surface. The liquid's surface behaves like a stretched membrane, and when disturbed, it tends to return the object to its original position, creating a restoring force. The other choices are incorrect: A buoyant force acts on objects submerged in a fluid, not floating on the surface; pressure differences usually affect sinking objects, not floating ones; drag force is a resistance force that opposes motion, not related to surface tension.
2. The specific heat capacity of water is about 2 J/g°C. How much energy would you need to heat 1 kilogram of water by 10°C?
- A. 420 J
- B. 4,200 J
- C. 42,000 J
- D. 420,000 J
Correct answer: C
Rationale: The formula to calculate the energy required to heat a substance is Q = m × c × ΔT, where m is the mass, c is the specific heat capacity, and ΔT is the change in temperature. Given that 1 kilogram of water is equal to 1,000 grams, the mass (m) is 1,000 g, the specific heat capacity (c) of water is 4.2 J/g°C (not 2 J/g°C), and the change in temperature (ΔT) is 10°C. Substituting these values into the formula: Q = 1,000 × 4.2 × 10 = 42,000 J. Therefore, the correct energy required to heat 1 kilogram of water by 10°C is 42,000 J. Choices A, B, and D are incorrect as they do not consider the correct specific heat capacity of water or the conversion of mass to grams.
3. Electric motors convert electrical energy primarily into:
- A. Thermal energy
- B. Light
- C. Mechanical energy
- D. Sound waves
Correct answer: C
Rationale: Electric motors convert electrical energy into mechanical energy. When electricity passes through the coils in the motor, it creates a magnetic field that interacts with the field from the permanent magnets, resulting in a force that drives motion. Choice A, 'Thermal energy,' is incorrect as electric motors are designed to minimize heat production. Choice B, 'Light,' is incorrect as electric motors do not produce light as a primary output. Choice D, 'Sound waves,' is incorrect as the primary output of an electric motor is mechanical motion, not sound waves.
4. A 120-volt heat lamp draws 25 amps of current. What is the lamp’s resistance?
- A. 96 ohms
- B. 104 ohms
- C. 150 ohms
- D. 4.8 ohms
Correct answer: D
Rationale: To find the resistance of the lamp, we use Ohm’s Law, which states that resistance (R) is equal to voltage (V) divided by current (I), expressed as: R = V / I. Given that the voltage (V) is 120 volts and the current (I) is 25 amps, we substitute these values into the formula: R = 120 V / 25 A = 4.8 ohms. Therefore, the resistance of the lamp is 4.8 ohms. Choice A, 96 ohms, is incorrect as it is not the result of the correct calculation. Choice B, 104 ohms, is incorrect as it does not match the calculated resistance. Choice C, 150 ohms, is incorrect as it is not the correct resistance value obtained through the calculation.
5. An object with a mass of 45 kg has momentum equal to 180 kg⋅m/s. What is the object’s velocity?
- A. 4 m/s
- B. 8.1 km/s
- C. 17.4 km/h
- D. 135 m/s
Correct answer: A
Rationale: The momentum of an object is calculated by multiplying its mass and velocity. Mathematically, momentum = mass x velocity. Given that the mass is 45 kg and the momentum is 180 kg⋅m/s, we can rearrange the formula to solve for velocity: velocity = momentum / mass. Plugging in the values, velocity = 180 kg⋅m/s / 45 kg = 4 m/s. Therefore, the object's velocity is 4 m/s. Choices B, C, and D are incorrect because they do not align with the correct calculation based on the given mass and momentum values.
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