1.
Which of the following is not a unit for power?
Correct Answer
A. Joule â€“ second
Explanation
Power is the rate at which work is done or energy is transferred. It is measured in watts, which is equal to one joule of energy transferred per second. Therefore, joule - second is not a unit for power, as it represents the product of energy (joule) and time (second), rather than the rate of energy transfer. The other options, watt, newton-meter per second, and horsepower, are all valid units for power.
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 calculated using 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. Plugging in these values into the formula, we find that 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. Speed is a measure of how fast an object is moving, so if an object has kinetic energy, it must also have speed. Impulse, acceleration, and force are not necessarily required for an object to have kinetic energy.
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 large surface area and low mass, causing it to fall slower than 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. Force on the bullet acts for a longer distance
Explanation
The force on the bullet acts for a longer distance, which means that the bullet is accelerated over a longer period of time compared to the rifle. This results in a greater change in velocity for the bullet, and therefore a greater increase in kinetic energy. Since kinetic energy is directly proportional to the square of the velocity, the bullet ends up with more energy than the recoiling rifle.
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. Kinetic energy depends on the mass and velocity of the object, and it is directly proportional to the square of the velocity. Therefore, if an object is stationary or at rest, it does not have any kinetic energy.
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. In the case of speed, an object with high speed has a greater potential energy because it has the ability to do more work or cause more change. The speed of an object directly affects its potential energy, making it the correct answer in this context.
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 of the object. Therefore, if the object is raised twice as high, it will gain twice as much potential energy. This is because the potential energy is directly proportional to the height, so increasing the height by a factor of 2 will result in an increase in potential energy by the same factor of 2.
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. Therefore, if the object is lifted 20 meters instead of 10, its potential energy will be twice as much. This is because potential energy is calculated using the formula PE = mgh, where m is the mass of the object, g is the acceleration due to gravity, and h is the height. As the height is doubled, the potential energy will also double.
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 kinetic energy of an object is directly proportional to its velocity squared. Since the faster arrow has twice the kinetic energy of the slower arrow, it means that its velocity is square root of 2 times greater than the velocity of the slower arrow. The distance penetrated by an arrow is directly proportional to its velocity. 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 completely transformed into gravitational potential energy. However, when the ball returns to its original level, it encounters air resistance which causes some of its energy to be lost. Therefore, its kinetic energy when it returns to its original level is 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
D. Always true.
Explanation
The explanation for the given correct answer, "always true," is that the car radio requires electrical power to operate, which is generated by the car's engine. Therefore, regardless of whether the car's engine is running or stopped, the car radio will consume gasoline because the engine needs to be running to provide the necessary power. Hence, it is always true that a car will burn more gasoline if the car radio is turned on.
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 kinetic energy of an object is directly proportional to its velocity squared. Since the faster arrow has twice the speed of the slower arrow, it will have four times the kinetic energy. This increased energy will allow it to penetrate the hay bale four times deeper than the slower arrow.
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. This conversion can be done by multiplying the number of kilowatt-hours by 3.6. Since a kilowatt-hour is a unit of energy and a joule is also a unit of energy, the conversion between the two can be made. Therefore, the correct 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 the feather and the coin. Therefore, both objects experience the same gravitational force and fall with the same acceleration. This means that their accelerations are equal.