Which of the following best explains why an ice skater is able to coast on ice for a long distance without pushing off in a straight line across the ice?
- A. The force of friction on the blades of the skates is greater than the force of friction on the ice.
- B. The force of friction on the blades of the skates is less than the force of friction on the ice.
- C. The ice exerts a constant forward force on the skater.
- D. The buoyant force on the blades of the skates is greater than the weight of the skater.
Correct Answer & Rationale
Correct Answer: B
An ice skater can glide smoothly due to the minimal friction between the skate blades and the ice, which is significantly lower than the friction experienced on other surfaces. This reduced friction allows the skater to maintain momentum over longer distances without needing to push off. Option A is incorrect because it suggests greater friction on the blades, which would hinder movement. Option C is misleading, as the ice does not exert a forward force; instead, the skater continues moving due to existing momentum. Option D is also wrong; while buoyancy affects weight in water, it does not apply to ice skating, where weight and friction are the primary factors.
An ice skater can glide smoothly due to the minimal friction between the skate blades and the ice, which is significantly lower than the friction experienced on other surfaces. This reduced friction allows the skater to maintain momentum over longer distances without needing to push off. Option A is incorrect because it suggests greater friction on the blades, which would hinder movement. Option C is misleading, as the ice does not exert a forward force; instead, the skater continues moving due to existing momentum. Option D is also wrong; while buoyancy affects weight in water, it does not apply to ice skating, where weight and friction are the primary factors.
Other Related Questions
Which TWO of the following are true statements about hurricanes?
- A. They are typically over 160 kilometers, or 100 miles, in diameter.
- B. They form over cold water in Earth's polar regions and move slowly.
- C. They develop quickly and usually last for less than 30 minutes.
- D. They can have sustained wind speeds that are over 200 kilometers per hour.
Correct Answer & Rationale
Correct Answer: A, D
Hurricanes are vast systems, often exceeding 160 kilometers (100 miles) in diameter, making option A true. Additionally, they can reach sustained wind speeds over 200 kilometers per hour, confirming option D. In contrast, option B is incorrect as hurricanes form over warm waters, typically in tropical regions, not cold polar waters. Moreover, they do not move slowly; they can travel at significant speeds. Option C is also false; while hurricanes can develop rapidly, they generally last for several days, not just 30 minutes. Understanding these characteristics is crucial for recognizing the nature and impact of hurricanes.
Hurricanes are vast systems, often exceeding 160 kilometers (100 miles) in diameter, making option A true. Additionally, they can reach sustained wind speeds over 200 kilometers per hour, confirming option D. In contrast, option B is incorrect as hurricanes form over warm waters, typically in tropical regions, not cold polar waters. Moreover, they do not move slowly; they can travel at significant speeds. Option C is also false; while hurricanes can develop rapidly, they generally last for several days, not just 30 minutes. Understanding these characteristics is crucial for recognizing the nature and impact of hurricanes.
Which of the following best describes what happens when two magnets repel each other?
- A. The objects are pulled toward one another.
- B. The objects are pushed away from one another.
- C. An electric spark jumps from one object to another.
- D. Nothing happens until the objects are touched.
Correct Answer & Rationale
Correct Answer: B
When two magnets repel each other, they exert forces that push away from one another due to their like poles (north-north or south-south). This repulsion is a fundamental property of magnetism. Option A is incorrect because it describes attraction, which occurs when opposite poles (north-south) interact. Option C is misleading; electric sparks are not a typical result of magnet repulsion. Option D is also wrong, as repulsion occurs before any physical contact, demonstrating the active interaction between the magnets. Thus, the best description of this phenomenon is that the objects are pushed away from one another.
When two magnets repel each other, they exert forces that push away from one another due to their like poles (north-north or south-south). This repulsion is a fundamental property of magnetism. Option A is incorrect because it describes attraction, which occurs when opposite poles (north-south) interact. Option C is misleading; electric sparks are not a typical result of magnet repulsion. Option D is also wrong, as repulsion occurs before any physical contact, demonstrating the active interaction between the magnets. Thus, the best description of this phenomenon is that the objects are pushed away from one another.
An astronaut travels to the Moon, where the magnitude of the force of gravity is one-sixth the magnitude of the force of gravity on Earth. On the Moon, which of the following is true?
- A. The astronaut's mass is one-sixth of his mass on Earth.
- B. The astronaut's weight is one-sixth of his weight on Earth.
- C. The astronaut's mass is six times his mass on Earth.
- D. The astronaut's weight is six times his weight on Earth.
Correct Answer & Rationale
Correct Answer: B
An astronaut's mass remains constant regardless of location; therefore, option A is incorrect as mass on the Moon is the same as on Earth. Option C is also incorrect because mass does not change based on gravitational force. Option D misrepresents weight; weight is dependent on gravity, and since the Moon's gravity is one-sixth that of Earth's, the astronaut's weight is one-sixth, not six times. Thus, option B accurately reflects that the astronaut's weight on the Moon is one-sixth of his weight on Earth, aligning with the relationship between weight and gravitational force.
An astronaut's mass remains constant regardless of location; therefore, option A is incorrect as mass on the Moon is the same as on Earth. Option C is also incorrect because mass does not change based on gravitational force. Option D misrepresents weight; weight is dependent on gravity, and since the Moon's gravity is one-sixth that of Earth's, the astronaut's weight is one-sixth, not six times. Thus, option B accurately reflects that the astronaut's weight on the Moon is one-sixth of his weight on Earth, aligning with the relationship between weight and gravitational force.
A teacher is introducing the geologic time scale to third-grade students. She tells them that the entire history of Earth, from its formation to the present day, was 24 hours long, with 12:00 midnight representing the time of the formation of Earth and 12:00 midnight the following night representing the present day. About what time did humans appear in this 24-hour time scale?
- A. 11:58 PM
- B. 9:00 PM
- C. 6:00 PM
- D. 1:00 PM
Correct Answer & Rationale
Correct Answer: A
In this 24-hour analogy of Earth's history, humans appeared very recently, approximately 200,000 years ago, which is just a fraction of the total time. This corresponds to 11:58 PM, indicating that humans emerged just two minutes before the "midnight" representing the present day. Option B (9:00 PM) suggests a much earlier appearance, which does not align with the scientific timeline of human evolution. Option C (6:00 PM) is even earlier, placing humans in a time when dinosaurs were still prominent. Option D (1:00 PM) is far too early, as it would imply humans existed when early mammals were just beginning to evolve. Thus, only 11:58 PM accurately reflects the brief time humans have existed in the context of Earth's history.
In this 24-hour analogy of Earth's history, humans appeared very recently, approximately 200,000 years ago, which is just a fraction of the total time. This corresponds to 11:58 PM, indicating that humans emerged just two minutes before the "midnight" representing the present day. Option B (9:00 PM) suggests a much earlier appearance, which does not align with the scientific timeline of human evolution. Option C (6:00 PM) is even earlier, placing humans in a time when dinosaurs were still prominent. Option D (1:00 PM) is far too early, as it would imply humans existed when early mammals were just beginning to evolve. Thus, only 11:58 PM accurately reflects the brief time humans have existed in the context of Earth's history.