HESI Physics

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.”