If every household in the US pledged to reduce their carbon footprint by the same amount as your family, how many tons of CO2 would we avoid putting into the atmosphere? (According to a 2011 report by the US Census Bureau, there are about 114,761,359 households in the US.) Show your calculations.

See below.  

Explanation:

1. Newton's first law

(a) Problem 1

What is the net force required to keep a 500 kg object moving with a constant velocity of 10 m·s?

Answer: None.

Explanation: An object in motion stays in motion unless a net force acts on it.

The object will keep moving at 10 m/s.

(b) Problem 2

A force of 20 N acts on a 10 kg object from the left. A force of 30 N acts on it from the right. What is the net force required to keep the object moving with a constant velocity of 10 m/s?

Answer: 20 N

Explanation:  

The net force is

30 N - 20 N = 10 N

You must apply another 10 N from the left. The net force is then:  

30 N - 30 N = 0

If there is no net force, the object will keep moving at 10 m/s.

2. Newton's second law

(a) Problem 1

What is the net force needed to accelerate an object at a constant 5 m·s⁻²?

Answer: 5 N

Explanation:

F = ma = 1 kg × 5 m·s⁻² = 5 kg·m·s⁻² = 5 N

(a) Problem 2

A net force of 2 N acts on a 1 kg object.  What is the magnitude and direction of the acceleration?

Answer: 2 m·s⁻²

Explanation:

F = ma

2 N = 1 kg × a

a = (2 N)/(1 kg) = (2 kg·m·s⁻²\1 kg) = 2 m·s⁻²

The direction of the acceleration is the same as that of the applied force.

2. Newton's third law

(a) Problem 1

A person with a mass of 58 kg is standing near you. Diagram and calculate the opposing forces.

Answer: 570 N up and down

Explanation:

See Fig. 1.  The person's mass exerts a downward force on the floor.

F = mg, where g is the acceleration due to Earth's gravity

F = 58 kg × 9.8 m·s⁻² = 570 kg·m·s⁻² = 570 N

The floor exerts an upward force of 570 N.

(a) Problem 2

A teacher (mass 65 kg) pushes a cart (mass = 12 kg) of equipment (mass = 7 kg). Her foot applies a force of 150 N backward on the floor against a frictional force of 24 N. Diagram the opposing forces and calculate the net force available to move the cart.

Answer: 126 N

Explanation:

See Fig. 2 below. The teacher's mass exerts a downward force W on the floor, which exerts an equal reaction force R upward. The cart and equipment also exert a downward force on the floor, which exerts the same force upward. We can ignore these forces because they do not contribute to forward motion.

The teacher's foot exerts a backward force of 150 N on the floor, which exerts an equal force forward. However, a frictional force of 24 N opposes the forward force.

The net external force is the force of the floor minus the opposing frictional force. Thus,

F = 150 N − 24 N = 126 N