Nokea
A 10-kg object moving at 5 m/s has an impulse acted on it causing the velocity to change to 15 m/s. What was the impulse that was applied to the object?
- A. 10 kgâ‹…m/s
- B. 15 kgâ‹…m/s
- C. 20 kgâ‹…m/s
- D. 100 kgâ‹…m/s
Correct Answer: D
Rationale: Impulse is the change in momentum of an object. The initial momentum is calculated as 10 kg 5 m/s = 50 kgâ‹…m/s, and the final momentum is 10 kg 15 m/s = 150 kgâ‹…m/s. The change in momentum (impulse) is 150 kgâ‹…m/s - 50 kgâ‹…m/s = 100 kgâ‹…m/s. Therefore, the impulse applied to the object is 100 kgâ‹…m/s. Choices A, B, and C are incorrect because they do not reflect the correct calculation of the impulse based on the change in momentum of the object.
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The buoyant force, F_b, experienced by an object submerged in a fluid is given by:
- A. F_b = W, the object's weight
- B. F_b = W_d, the weight of the fluid displaced by the object
- C. F_b = Ï, the density of the fluid
- D. F_b = V, the object's volume
Correct Answer: B
Rationale: The correct formula for the buoyant force experienced by an object submerged in a fluid is given by Archimedes' principle, which states that the buoyant force is equal to the weight of the fluid displaced by the object. This is represented by the formula F_b = W_d, where W_d is the weight of the fluid displaced by the object. This force acts in the opposite direction to gravity and is responsible for objects floating or sinking in fluids. Choice A is incorrect because the buoyant force is not equal to the object's weight. Choice C is incorrect because the density of the fluid is not directly related to the buoyant force. Choice D is incorrect because the object's volume is not the determining factor for the buoyant force.
A car, starting from rest, accelerates at 10 m/s² for 5 seconds. What is the velocity of the car after 5 seconds?
- A. 2 m/s
- B. 5 m/s
- C. 50 m/s
- D. The answer cannot be determined from the information given.
Correct Answer: C
Rationale: The velocity of an object can be calculated using the formula: final velocity = initial velocity + (acceleration time). In this case, the car starts from rest, so the initial velocity is 0 m/s. Given that the acceleration is 10 m/s² and the time is 5 seconds, we can plug these values into the formula to find the final velocity: final velocity = 0 m/s + (10 m/s² 5 s) = 0 m/s + 50 m/s = 50 m/s. Therefore, the velocity of the car after 5 seconds is 50 m/s. Choice A (2 m/s) and Choice B (5 m/s) are incorrect because they do not consider the acceleration the car undergoes over the 5 seconds, resulting in a final velocity greater than both. Choice D (The answer cannot be determined from the information given) is incorrect as the final velocity can be determined using the provided data and the kinematic equation.
Why are boats more buoyant in salt water than in fresh water?
- A. Salt decreases the mass of the boats.
- B. Salt increases the volume of the water.
- C. Salt affects the density of the boats.
- D. Salt increases the density of the water.
Correct Answer: D
Rationale: Salt increases the density of water, making saltwater more buoyant than freshwater. The higher density of saltwater provides more lift to a boat, enabling it to float more easily compared to in freshwater. Choice A is incorrect because salt does not affect the mass of the boats. Choice B is incorrect as salt does not increase the volume of water. Choice C is incorrect since salt affects the density of water, not the boats themselves. Therefore, the correct answer is that salt increases the density of the water, resulting in boats being more buoyant in salt water than in fresh water.
How might the energy use of an appliance be expressed?
- A. Power = energy time
- B. Time + energy = power
- C. Energy = power time
- D. Energy/power = time
Correct Answer: C
Rationale: The energy use of an appliance can be expressed using the formula Energy = Power Time. In this formula, Energy represents the amount of electricity consumed by the appliance, Power indicates the rate at which the appliance uses electricity (measured in watts), and Time represents the duration for which the appliance is being used (measured in hours). By multiplying the power rating of the appliance by the time it is in use, one can calculate the total energy consumed. Option C is the correct choice because it accurately represents the relationship between power, time, and energy. Choices A, B, and D present incorrect representations of the relationship between energy, power, and time, making them wrong answers.
Which vehicle has the greatest momentum?
- A. A 9,000-kg railroad car traveling at 3 m/s
- B. A 2,000-kg automobile traveling at 24 m/s
- C. A 1,500-kg MINI Coupe traveling at 29 m/s
- D. A 500-kg glider traveling at 89 m/s
Correct Answer: D
Rationale: The momentum of an object is calculated by multiplying its mass by its velocity. The momentum formula is p = m v, where p is momentum, m is mass, and v is velocity. Comparing the momentum of each vehicle: A: 9,000 kg 3 m/s = 27,000 kg·m/s B: 2,000 kg 24 m/s = 48,000 kg·m/s C: 1,500 kg 29 m/s = 43,500 kg·m/s D: 500 kg 89 m/s = 44,500 kg·m/s. Therefore, the glider (500-kg) traveling at 89 m/s has the greatest momentum of 44,500 kg·m/s, making it the correct choice. Options A, B, and C have lower momentum values compared to option D, proving that the 500-kg glider traveling at 89 m/s has the highest momentum among the given vehicles.