1.
Which of the following is not a unit for power?
Correct Answer
D. Both A and C
Explanation
A joule-second represents the unit of angular momentum, not power. Newton meter is a unit of torque, which is a measure of rotational force, not power. Newton-metre is simply a different notation for the same unit of torque. Power is typically measured in watts (W), and these other units represent different physical quantities related to energy, force, or torque.
2.
Car A has a mass of 1000 kg and a speed of 60 km/h, and car B has a mass of 2000 kg and a speed of 30 km/h. The kinetic energy of car A is _____.
Correct Answer
C. Twice that of car B
Explanation
The kinetic energy of an object is given by the formula KE = 1/2 * mass * velocity^2. Car A has a mass of 1000 kg and a speed of 60 km/h, while car B has a mass of 2000 kg and a speed of 30 km/h. By plugging in the values into the formula, we can calculate the kinetic energy of car A and car B. The kinetic energy of car A is twice that of car B.
3.
If an object has kinetic energy, then it also must have _____.
Correct Answer
A. Speed
Explanation
If an object has kinetic energy, it means that it is in motion. The amount of kinetic energy an object has depends on its mass and velocity. Therefore, in order for an object to have kinetic energy, it must also have speed.
4.
A feather and a coin are dropped in the air. Each falls with equal _____.
Correct Answer
D. None of the above
Explanation
When a feather and a coin are dropped in the air, they do not fall with equal momenta, kinetic energies, or potential energy. The feather experiences more air resistance due to its larger surface area and lighter weight, causing it to fall more slowly and with less momentum and kinetic energy compared to the coin. Therefore, the correct answer is "none of the above."
5.
When a bullet is fired from a rifle, the force on the rifle is equal to the force on the bullet. However, the energy of the bullet is greater than the energy of the recoiling rifle because the _______.
Correct Answer
A. Mass of the bullet is much smaller than the mass of the rifle
Explanation
According to the law of conservation of momentum, the total momentum of the system (bullet and rifle) remains constant. When the bullet is fired, it gains a significant velocity due to its smaller mass, resulting in a higher kinetic energy. In contrast, the rifle, being much more massive, experiences a smaller velocity in the opposite direction, leading to lower kinetic energy. While the forces exerted on the bullet and the rifle are equal and opposite (action and reaction), the kinetic energy depends on both mass and velocity, resulting in the bullet having greater energy.
6.
An object that has kinetic energy must be _____.
Correct Answer
A. Moving.
Explanation
An object that has kinetic energy must be moving because kinetic energy is the energy possessed by an object due to its motion. If an object is at rest, it does not have any kinetic energy. However, if the object is moving, it possesses kinetic energy which is dependent on its mass and velocity. Therefore, for an object to have kinetic energy, it must be in motion.
7.
An object that has potential energy has this energy because of its _____.
Correct Answer
A. Speed.
Explanation
An object that has potential energy has this energy because of its speed. Potential energy is the energy possessed by an object due to its position or condition, and it can be converted into other forms of energy, such as kinetic energy. The speed of an object affects its potential energy because the faster it moves, the more kinetic energy it has, which in turn increases its potential energy. Therefore, the speed of an object is directly related to its potential energy.
8.
An object is raised above the ground gaining a certain amount of potential energy. If the same object is raised twice as high it gains _____.
Correct Answer
B. Twice as much potential energy.
Explanation
When an object is raised above the ground, it gains potential energy due to its increased height. The potential energy is directly proportional to the height. Therefore, if the object is raised twice as high, it will gain twice as much potential energy. This is because potential energy is directly proportional to the height and doubling the height will result in doubling the potential energy.
9.
When an object is lifted 10 meters, it gains a certain amount of potential energy. If the same object is lifted 20 meters, its potential energy is ______.
Correct Answer
C. Twice as much.
Explanation
When an object is lifted, its potential energy is directly proportional to the height it is lifted to. The potential energy is given by the equation PE = mgh, where m is the mass of the object, g is the acceleration due to gravity, and h is the height. Since the height is doubled from 10 meters to 20 meters, the potential energy will also double, resulting in twice as much potential energy. Therefore, the correct answer is "twice as much."
10.
Two identical arrows, one with twice the kinetic energy of the other, are fired into a hay bale. The faster arrow will penetrate _____.
Correct Answer
B. Twice as far as the slower arrow.
Explanation
The faster arrow will penetrate twice as far as the slower arrow because kinetic energy is directly proportional to the square of the velocity. Since the faster arrow has twice the kinetic energy of the slower arrow, it means that its velocity is âˆš2 times greater than the slower arrow. Therefore, the faster arrow will penetrate twice as far as the slower arrow.
11.
A ball is projected into the air with 100 J of kinetic energy which is transformed to gravitational potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is _____.
Correct Answer
A. Less than 100 J.
Explanation
When the ball is projected into the air, it has 100 J of kinetic energy. As it reaches the top of its trajectory, this kinetic energy is transformed into gravitational potential energy. However, when the ball returns to its original level after encountering air resistance, some of its energy is lost due to the work done against the resistance. Therefore, its kinetic energy will be less than the initial 100 J.
12.
Strictly speaking, a car will burn more gasoline if the car radio is turned on. This statement is _____.
Correct Answer
A. Totally false.
Explanation
The car radio consumes a negligible amount of power compared to the engine's operation. Most modern car radios use very little energy, typically in the range of a few watts. In comparison, the engine consumes gasoline to generate power for propulsion, which requires significantly more fuel.
Therefore, the power consumption of the car radio has a negligible impact on fuel consumption. The primary factor influencing fuel consumption is the engine's operation, not the operation of auxiliary devices like the radio.
13.
Two identical arrows, one with twice the speed of the other, are fired into a hay bale. The faster arrow will penetrate _____.
Correct Answer
C. Four times as far as the slower arrow.
Explanation
The faster arrow will penetrate four times as far as the slower arrow because the force of impact is directly proportional to the square of the velocity. Since the faster arrow has twice the speed of the slower arrow, it will have four times the force and therefore penetrate four times as far.
14.
How many Joules of energy are in one kilowatt-hour?
Correct Answer
D. 3.6 megajoules
Explanation
One kilowatt-hour is equal to 3.6 megajoules of energy. This is because a kilowatt-hour is a unit of energy commonly used in electricity billing, and it represents the amount of energy consumed by a device with a power output of one kilowatt over the course of one hour. One kilowatt-hour is equivalent to 3.6 million joules, hence the answer is 3.6 megajoules.
15.
A feather and a coin dropped in a vacuum fall with equal _____.
Correct Answer
C. Accelerations
Explanation
In a vacuum, there is no air resistance or other external forces acting on objects. Therefore, both the feather and the coin would experience the same acceleration due to gravity, which is approximately 9.8 m/s^2. This means that they would fall with equal accelerations.