Hesi Physics Questions With Answers and Explanations

HESI Physics Questions with Answers and Explanations 1. When a junked car is compacted, which statement is true? A. Its mass increases. B. Its mass decreases. C. Its density increases. D. Its density decreases. Exp ...

HESI Physics Questions with Answers and Explanations 1. When a junked car is compacted, which statement is true? A. Its mass increases. B. Its mass decreases. C. Its density increases. D. Its density decreases. Explanation: Since density = mass/volume, it should be obvious that the decrease in volume as a car is crushed should lead to an increase in density. Nothing happens to change the mass of the car. 2. A car travels 3 miles north, 6 miles south, 2 miles east, 2 miles west, and then 3 miles north. Which of the following is true? A. The displacement of the car is 16 miles, and the distance traveled is 0 miles. B. The displacement of the car is 16 miles, and the distance traveled is 16 miles. C. The displacement of the car is 0 miles, and the distance traveled is 0 miles. D. The displacement of the car is 0 miles, and the distance traveled is 16 miles. Expalanation: If a car travels 3 miles north, 6 miles south, 2 miles east, 2 miles west, and then 3 miles north, it has traveled a total distance of 16 miles. However, because of the directions it has traveled, it has ended up in the place where it started, giving it a displacement of 0. 3. Why doesn’t a raindrop accelerate as it approaches the ground? A. Gravity pulls it down at a constant rate. B. Air resistance counteracts the gravitational force. C. Its mass decreases, decreasing its speed. D. Objects in motion decelerate over distance. Explanation: Gravity in fact causes acceleration, making choice A incorrect— unless air resistance counteracts that acceleration, which it may easily do for an object as small and lightweight as a raindrop. Raindrops may lose mass (choice C), but that would not decrease their acceleration. Choice D violates Newton’s first law. 4. An object moves 100 m in 10 s. What is the velocity of the object over this time? A. 10 m/s B. 90 m/s C. 110 m/s D. 1,000 m/s Explanation: Velocity is the change in distance over time. 100 m/10 s is the same as 10 m/s. 5. Which of these objects has the greatest momentum? A. A 1,250-kg car moving at 5 m/s B. An 80-kg person running at 4 m/s C. A 10-kg piece of meteorite moving at 600 m/s D. A 0.5-kg rock moving at 40 m/s Explanation: Momentum is calculated by multiplying mass by velocity, p = mv. Although the meteorite seems intimidating, it is the car that has the greatest momentum, at 6,250 kg⋅m/s. 6. Sublimation is the change in matter from solid to gas or gas to solid without passing through a liquid phase. Outside of the laboratory, which solid provides the best example of this? A. Iron B. Silver C. Salt crystal D. Dry ice Explanation: Dry ice is frozen carbon dioxide. As it breaks down, it transforms directly into gas without passing through a liquid phase. Sublimation of metals is possible, but not “outside of the laboratory.” 7. A 1.0-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. Explanation: Applying Newton’s second law, F = ma, a 1.0-kg block accelerated at 6 m/s2 requires a 6-N force to move it. 8. A 60-watt lightbulb is powered by a 110-volt power source. What is the current being drawn? A. 0.55 amperes B. 1.83 amperes C. 50 amperes D. 6,600 amperes Explanation: The equation P = IV, power equals current times voltage, is the one to use. Dividing the power by the voltage gives you I = P/V, and 60 watts/110 volts equals approximately 0.55 amperes. 9. A wave moves through its medium at 20 m/s with a wavelength of 4 m. What is the frequency of the wave? A. 5 s−1 B. 16 s−1 C. 24 s−1 D. 80 s−1 Explanation: According to the equation v = fl, frequency is equal to the velocity of the wave divided by the wavelength. Dividing 20 m/s by 4 m gives you 5 s−1. 10. 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. Explanation: When the car is attached to the electromagnet, its potential energy (PE) is 367.5 kJ because PE = mgh, or (1,500 kg)(9.8 m/s2)(25 m). As the car falls, all 367.5 kJ of PE are converted to kinetic energy. On hitting the ground and making a sound, the car will no longer possess any PE. 11. Why does potential energy increase as particles approach each other? A. Attractive forces increase. B. Attractive forces decrease. C. Repulsive forces increase. D. Repulsive forces decrease. Explanation: Unlike charges attract each other; like charges repel each other. As two like charges near each other, work is required to push them together, and potential energy increases. 12. A transverse wave does not have . A. a compression B. an amplitude C. a frequency D. a wavelength Explanation: Transverse waves do not have areas of compression and expansion as they move perpendicular to the direction of the wave. 13. How do a scalar quantity and a vector quantity differ? A. A scalar quantity has both magnitude and direction, and a vector does not. B. A scalar quantity has direction only, and a vector has only magnitude. C. A vector has both magnitude and direction, and a scalar quantity has only magnitude. D. A vector has only direction, and a scalar quantity has only magnitude. Explanation: A vector quantity, for example, 25 k/h N, has both magnitude and direction. A scalar quantity has only magnitude. 14. Which one has the highest density? A. Mist B. Water C. Steam D. Ice Explanation: Ice (choice D) floats on water (choice B) because its density is less, despite the fact that it is a solid. When water freezes, its volume increases, making its density (mass/volume) less. 15. Two objects attract each other with a gravitational force of 12 units. If you double the distance between the objects, what is the new force of attraction between the two? A. 3 units B. 6 units C. 24 units D. 48 units Explanation: Increasing distance by a factor of 2 decreases the force by a factor of 22, or 4. The new force of attraction is the original force divided by 4, or 3 units. 16. What is the purpose of a switch in a circuit? A. To reverse the direction of alternating current B. To increase the voltage of the batter or cell C. To increase the resistance of wires in the circuit D. To allow the circuit to open and close Explanation: The switch interrupts the electrical circuit or allows the current to flow from one conductor to another. 17. 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 Explanation: Gay-Lussac’s law states that temperature and pressure are directly proportional. Heat from friction caused as tires rub on the road increases the temperature of the air in the tire, causing an increase in pressure. This is why you are advised to measure the pressure in your tires when they are cold—before starting a trip. 18. A 5-cm candle is placed 20 cm away from a concave mirror with a focal length of 15 cm. About what is the image height of the candle in the mirror? A. 30.5 cm B. 15.625 cm C. −15 cm D. −30.5 cm Explanation: (C) You are looking first at the relationship between the object distance (do ), the image distance (di ), and the focal length (f). Start out with 1/f = 1/do + 1/di where f = 15 cm and do = 20 cm. In this case, Use equivalent fractions to solve: Now you can use what you know to calculate the image height (hi ), using where ho = 5 cm, do = 20 cm, and di = 60 cm. So meaning that the image height is −15 cm. The negative value indicates an inverted image. 19. A plucked guitar string makes 80 vibrations in one second. What is the period? A. 0.0125 s B. 0.025 s C. 0.125 s D. 0.25 s Explanation: The period is the reciprocal of the frequency. Here, the frequency is 80 vibrations per second. The period is 1/80, or 0.0125 s. 20. A 2,000-kg car travels at 15 m/s. For a 1,500-kg car traveling at 15 m/s to generate the same momentum, which would need to happen? A. It would need to accelerate to 20 m/s. B. It would need to add 500 kg in mass. C. Both A and B D. Either A or B Explanation: Momentum is the product of velocity and mass. The first car’s momentum is 2,000 × 15 = 30,000 kg⋅m/s. The second car’s momentum is 1,500 × 15 = 22,500 kg⋅m/s. For its momentum to equal that of the first car, it could either accelerate to 20 kg/s or add 500 kg to its mass. 21. Given the four wires described here, which would you expect to have the greatest resistance? A. 1 km of American wire gauge 1; diameter 7.35 mm B. 1 km of American wire gauge 2; diameter 6.54 mm C. 1 km of American wire gauge 3; diameter 5.83 mm D. 1 km of American wire gauge 4; diameter 5.19 mm Explanation: Resistance of a wire depends on length, material, and cross- sectional area. Given four wires of the same length and material, the thinnest wire would have the highest resistance. 22. A 5-kg block is suspended from a spring, causing the spring to stretch 10 cm from equilibrium. What is the spring constant for this spring? A. 4.9 N/cm B. 9.8 N/cm C. 49 N/cm D. 50 N/cm Explanation: The equation to use is K = f/x, where K is the spring constant, f is force, and x is distance. First, find the force in Newtons. Since the gravitational constant on Earth is 9.8, multiply the mass, 5, by that constant to find the force: 9.8 × 5 = 49 N. Now calculate the spring constant: K = 49 N/10 cm. K = 4.9 N/cm. 23. A 1,000-kg car drives at 10 m/s around a circle with a radius of 50 m. What is the centripetal acceleration of the car? A. 2 m/s2 B. 4 m/s2 C. 5 m/s2 D. 10 m/s2 Explanation: Determine the acceleration by dividing the speed squared by the radius of the track: a = v2/R. In this case, a = 100/50, or 2 m/s2. 24. A 3-volt flashlight uses a bulb with 60-ohm resistance. What current flows through the flashlight? A. 0.05 amp B. 0.5 amp C. 1.8 amp D. 18 amp Explanation: According to Ohm’s law, current (I) equals voltage (ΔV) divided by resistance (R), or I = ΔV/R. In this case, you know voltage and resistance, so I = 3/60, or 0.05 amp. 25. A balloon with a charge of 5 μC is placed 25 cm from another balloon with the same charge. What is the magnitude of the resulting repulsive force? A. 0.18 N B. 1.8 N C. 10−3 N D. 5 × 10−3 N Explanation: Use Coulomb’s law to find the force. The equation to use is this: Remember that 1 coulomb = 106 microcoulombs. Both balloons in this problem have the same charge, so Q1 and Q2 in this case equal 5 × 10−6 C, and d, distance, = 25 cm, or 0.25 m. Now, you must recall Coulomb’s constant, k = (9.0 × 109 N⋅m2 /C2 ). From this point, it’s all about computation: