Question 1

A force of 100 N is applied to a 50-kg mass in the direction of motion for a distance of 6.0 m and then the force is increased to 150 N for the next 4.0 m.For the 10 m of travel, how much work is done by the varying force?

Accepted Answer

To calculate the work done by the varying force, we need to calculate the work done in two parts:
1) Work done by the 100 N force for 6.0 m
2) Work done by the 150 N force for 4.0 m

For the first part, we can use the formula:
Work = force x distance x cos(theta)
where theta is the angle between the force and the direction of motion (which is 0 degrees in this case).

Work = 100 N x 6.0 m x cos(0)
Work = 600 J

For the second part, we can use the same formula:
Work = force x distance x cos(theta)
But this time, the force is 150 N and the distance is 4.0 m.

Work = 150 N x 4.0 m x cos(0)
Work = 600 J

Therefore, the total work done by the varying force is:
Total work = 600 J + 600 J
Total work = 1 200 J

Therefore, the best choice is A) 1 200 J.

Question 2

The unit of power, watt, is dimensionally the same as:

Accepted Answer

The unit watt is defined as one joule of energy expended per second of time. Therefore, watt is equivalent to joules per second, or joule/second. Choice A has the correct units, but the wrong order (it should be seconds/joule). Choice C is joule-meter, which is the unit for work or energy, not power. Choice D is joule/meter, which does not have a defined physical quantity.

Question 3

Water flows over a section of Niagara Falls at a rate of 1.20 * 10⁶ kg/s and falls 50.0 m.What is the power dissipated by the waterfall?

Accepted Answer

The power dissipated by the waterfall can be calculated as the product of the water's weight, its height of fall, and the acceleration due to gravity. Therefore,

Power dissipated = (1.20 * 10^16 kg/s) * (50.0 m) * (9.81 m/s^2) = 588 MW

Therefore, the best choice for the power dissipated by the waterfall is A) 588 MW.

Question 4

The net force acting on a 6.0-kg object is given by F_x = (10 - x) N, where F_x is in newtons and x is in meters.How much work is done on the object as it moves from x = 0 to x = 10 m?

Accepted Answer

The work done is equal to the area under the force vs distance graph. 
So, work = ∫(10-x)dx within limits from 0 to 10.
 
∫(10-x)dx = [10x - 0.5x^2] within limits from 0 to 10
 
= [10(10) - 0.5(10)^2] - [10(0) - 0.5(0)^2]
 
= 50 J. 
 
Therefore, the answer is (C) 50 J.

Question 5

The net force acting on a 12.6-kg object is given by F_x = (20 - x) N, where F_x is in newtons and x is in meters.How much work is done on the object as it moves from x = 0 to x = 10 m?

Accepted Answer

The work done on an object is given by the formula:

W = ∫Fdx

where F is the force acting on the object and x is the distance moved by the object.
So, we need to integrate the given force expression with respect to x from 0 to 10 m.

W = ∫(20 - x) dx from x = 0 to x = 10
W = [20x - (x^2)/2] from x = 0 to x = 10
W = [20(10) - (10^2)/2] - [20(0) - (0^2)/2]
W = 200 - 0
W = 200 J

Therefore, the work done on the object as it moves from x = 0 to x = 10 m is 200 J. Hence, the best choice is C) 150 J.

Question 6

A 100-W light bulb is left on for 10.0 hours.Over this period of time, how much energy was used by the bulb?

Accepted Answer

The formula to calculate energy is:
Energy (in joules) = Power (in watts) x Time (in seconds)
We need to convert 10.0 hours to seconds by multiplying it by 3600 (60 seconds x 60 minutes).
10.0 hours x 3600 seconds/hour = 36,000 seconds
Now we can use the formula:
Energy = 100 watts x 36,000 seconds
Energy = 3,600,000 joules or 3.6 MJ (megajoules).
Therefore, the correct answer is C) 3,600,000 J.

Question 7

Is it possible for the total mechanical energy of a moving particle to be negative?

Accepted Answer

The total mechanical energy of a moving particle can be negative if its potential energy is more negative than its kinetic energy is positive. This could occur if the particle is moving in a region of space with a strong gravitational field, for example, or if there is an attractive force acting on the particle that outweighs its kinetic energy. Friction is not a necessary condition for the total mechanical energy of a particle to be negative.

Question 8

The rate at which work is done is equivalent to which of the following?

Accepted Answer

The rate at which work is done is known as power, which is typically measured in watts or horsepower. The other choices - increase in potential energy, thermal energy, and potential energy - are all forms of energy, but they do not directly relate to the rate at which work is done.

Question 9

A jet engine develops 1.0 * 10⁵ N of thrust in moving an airplane forward at a speed of 900 km/h.What is the power developed by the engine?

Accepted Answer

- First, we need to convert the speed of the airplane from km/h to m/s:
900 km/h = (900 x 1000) / 3600 = 250 m/s
- The power developed by the engine can be calculated using the formula:
power = force x velocity
- We have the force (thrust) in newtons and the velocity in m/s, so we can simply multiply them:
power = 1.0 * 10^15 N x 250 m/s = 2.5 * 10^17 W
- However, the answer choices are in units of megawatts (MW), so we need to convert our answer:
2.5 * 10^17 W = 2.5 * 10^14 MW
- The closest answer choice is C, 25 MW, so that is our final answer.

Question 10

A 60-kg woman runs up a flight of stairs having a rise of 4.0 m in a time of 4.2 s.What average power did she supply?

Accepted Answer

The answer of A 60-kg woman runs up a flight...

Question 11

A 200-hp engine can deliver, in SI units, an average power of ____.(1 hp = 746 W)

Accepted Answer

1 hp = 746 W
Therefore, 200 hp = 200 x 746 W = 149,200 W
Taking into account significant figures, the answer is 149,000 W.

Question 12

The area under the force vs.displacement curve represents:

Accepted Answer

The area under the force vs. displacement curve represents the work done by the force, which is equal to the force multiplied by the displacement. Therefore, the correct choice is C, work.

Question 13

The quantity of work equal to one joule is also equivalent to which of the following?

Accepted Answer

The answer of The quantity of work equal to one...

Question 14

Yuri, a Russian weightlifter, is able to lift 250 kg 2.00 m in 2.00 s.What is his power output?

Accepted Answer

The answer of Yuri, a Russian weightlifter, is able to...

Question 15

A force of 5.0 N is applied to a 20-kg mass on a horizontal frictionless surface.As the speed of the mass increases at a constant acceleration, the power delivered to it by the force:

Accepted Answer

Power = Force x Velocity. As the speed of the mass increases, so does its velocity. Therefore, the power delivered to the mass by the force increases.

Question 16

A speed boat requires 80 kW to move at a constant speed of 15 m/s.What is the resistive force of the water at this speed?

Accepted Answer

The answer of A speed boat requires 80 kW to...

Question 17

A 1 000-kg sports car accelerates from zero to 25 m/s in 7.5 s.What is the average power delivered by the automobile engine?

Accepted Answer

The average power delivered by the automobile engine can be calculated using the formula:

average power = work done / time taken

The work done by the engine is equal to the change in kinetic energy of the car:

work done = (1/2) * mass * (final velocity)^2 - (1/2) * mass * (initial velocity)^2

work done = (1/2) * 1000 kg * (25 m/s)^2 - (1/2) * 1000 kg * (0 m/s)^2

work done = 312,500 J

The time taken is given as 7.5 s.

Therefore,

average power = 312,500 J / 7.5 s

average power = 41,667 W

Converting to kilowatts:

average power = 41.7 kW

Therefore, the best choice is C.

Question 18

Three different mass projectiles are launched from the top of a building each at different angles of elevation.Each particle has the same initial kinetic energy.Which particle has the greatest speed just as it impacts with the ground?

Accepted Answer

The initial kinetic energy of each particle does not depend on its mass or angle of elevation. However, the speed at impact will depend on the mass of the particle since we can assume that air resistance is negligible. The particle with the lowest mass will have the greatest speed at impact.

Question 19

An automobile delivers 30.0 hp to its wheels when moving at a constant speed of 22.0 m/s.What is the resistance force on the automobile at this speed? (1 hp = 746 watts)

Accepted Answer

The answer of An automobile delivers 30.0 hp to its...

Question 20

Three different mass projectiles are launched from the top of a building each at different angles of elevation.Each particle has the same initial kinetic energy.Which particle has the greatest kinetic energy just as it impacts with the ground?

Accepted Answer

The answer of Three different mass projectiles are launched from...

Quiz 5: Energy