Answer: D. An action-reaction force pair
Explanation: When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body. There are two forces resulting from this interaction - a force on the chair and a force on your body. Another example would be a person pushing against a wall (action force), and the wall exerts an equal and opposite force against the person.
The force needed to accelerate an elevator upward at a rate of 
is 2000 N or 2 kN.
<u>Explanation:
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As per Newton's second law of motion, an object's acceleration is directly proportional to the external unbalanced force acting on it and inversely proportional to the mass of the object.
As the object given here is an elevator with mass 1000 kg and the acceleration is given as , the force needed to accelerate it can be obtained by taking the product of mass and acceleration.
So 2000 N or 2 kN amount of force is needed to accelerate the elevator upward at a rate of .
Answer:
a. True
Explanation:
Solar radiation at frequencies of visible light passes through the atmosphere, heating the planet's surface, subsequently this energy is emitted in infrared thermal radiation. This radiation is absorbed by the gases produced by the combustion of fossil fuels. Therefore, the greater the amount of these gases in the atmosphere, the more heat will be trapped in the earth, raising its global temperature.
