1.
The units of power are:
Correct Answer
A. Watts
Explanation
The units of power are measured in watts. Watts represent the rate at which energy is transferred or work is done. It is named after James Watt, a Scottish engineer who made significant contributions to the development of the steam engine. Watts are commonly used to measure electrical power, but can also be used to measure other forms of power such as mechanical or thermal power.
2.
A constant force of 10 N causes a box to move at a constant speed of 2 m/s. How much power is done in 10 seconds?
Correct Answer
B. 20W
Explanation
The power is calculated by multiplying the force applied to an object by the object's velocity. In this case, the constant force is 10 N and the constant speed is 2 m/s. Thus, the power is 10 N x 2 m/s = 20 W.
3.
Power is defined as:
Correct Answer
D. Work per unit time (W/t)
Explanation
The correct answer is "Work per unit time (W/t)". Power is defined as the rate at which work is done or the amount of work done per unit time. It represents how quickly energy is transferred or converted. Therefore, power is calculated by dividing the amount of work done by the time taken to do that work.
4.
How is work related to acceleration?
Correct Answer
C. W = m∙a∙d
Explanation
The equation W = m∙a∙d represents the work done on an object. In this equation, W represents work, m represents mass, a represents acceleration, and d represents distance. The equation shows that work is directly proportional to both mass and acceleration, as well as the distance over which the force is applied. This means that as either mass or acceleration increases, the amount of work done also increases. Similarly, if the distance over which the force is applied increases, the amount of work done also increases. Therefore, the equation W = m∙a∙d accurately represents the relationship between work and acceleration.
5.
In a period of 10 seconds, an elevator lifts a weight of 1000 N a distance of 10 m at constant velocity. What is the average power of the elevator over this time?
Correct Answer
A. 1000W
Explanation
The average power of the elevator can be calculated by dividing the work done by the elevator by the time taken. In this case, the work done is equal to the force applied (1000N) multiplied by the distance covered (10m), which is 10000J. The time taken is 10 seconds. Therefore, the average power is 10000J/10s = 1000W.
6.
Liz throws a softball with a force of 63 N a distance of 25 m. Jamie throws the softball with the twice amount of force, but the ball only goes 17 m. Which girl does less work?
Correct Answer
B. Liz
Explanation
Liz does less work because work is calculated by multiplying force and distance. Since Liz throws the softball with a force of 63 N and a distance of 25 m, her work is 63 N * 25 m = 1575 Nm. On the other hand, Jamie throws the softball with twice the force (126 N) but the ball only goes 17 m. Therefore, Jamie's work is 126 N * 17 m = 2142 Nm, which is greater than Liz's work. Therefore, Liz does less work.
7.
A machine using a power of 1000W requires a force of 100 N to raise a mass in 10 s. The height the mass is raised in this time is
Correct Answer
D. 100m
Explanation
The work done by a machine can be calculated by multiplying the force applied by the distance over which the force is applied. In this case, the force required is 100 N and the time taken is 10 seconds. Since power is equal to work divided by time, we can calculate the work done by the machine as 1000W x 10s = 10000 J. Given that the force required is 100 N, we can use the formula work = force x distance to find the distance. Rearranging the formula, we get distance = work / force = 10000 J / 100 N = 100 m. Therefore, the height the mass is raised in this time is 100 meters.
8.
How much energy is needed to run a 75-watt light bulb for 6 seconds?
Correct Answer
C. 450J
Explanation
The energy needed to run a light bulb can be calculated using the formula E = P * t, where E is the energy, P is the power, and t is the time. In this case, the power of the light bulb is given as 75 watts, and the time is given as 6 seconds. Plugging these values into the formula, we get E = 75 watts * 6 seconds = 450 joules. Therefore, the correct answer is 450J.
9.
A student is running up 3 flights of stairs. He runs up the first flight quickly but the last two he tires so goes a little slower. When does he exert more power and why?
Correct Answer
B. The first flight because he takes less time
Explanation
The student exerts more power on the first flight because he takes less time to complete it. Power is defined as the rate at which work is done or energy is transferred. Since the student is running up the stairs quickly on the first flight, he is doing work at a faster rate, resulting in more power exerted.
10.
An escalator is used to move 20 passengers every minute from the first floor of a department store to the second. The second floor is located 5.20 meters above the first floor. The average passenger's mass is 54.9 kg. Determine the POWER requirement of the escalator in order to move this number of passengers in one minute.
Correct Answer
D. 951.6 Watts
Explanation
The power requirement of the escalator can be calculated using the formula: Power = Work / Time. The work done by the escalator is equal to the force applied (mass of passengers multiplied by acceleration due to gravity) multiplied by the distance traveled (height of the second floor). The time taken is given as one minute. Plugging in the values, we can calculate the power requirement to be 951.6 Watts.