<u>Answer:</u>
Positive acceleration is in third hour and negative acceleration is in second hour.
<u>Explanation:</u>
Velocity of car in first hour = 70 mph
Velocity of car in second hour = 60 mph
Velocity of car in third hour = 80 mph
Acceleration = Change in velocity / Time
Acceleration in second hour = (60 - 70)/1 = -10 mph²
Acceleration in third hour = (80 - 60)/1 = 20 mph²
So positive acceleration is in third hour and negative acceleration is in second hour.
Answer:
Gravitational energy and kinetic energy
Answer: The copper wiring most likely caused the mini-refrigerator fire.
Explanation: A mini-refrigerator may have one or more evaporator fan motors. These motors have copper wiring. In some situation these copper wires gets overheated. It may result to the firing of the mini-refrigerator.
Therefore, the mini-refrigerator fire was most likely caused by copper wiring.
When an object is falling and reaches a constant velocity, the net force on the object is <em>zero</em> (it's not accelerating), and the weight of the object is equal to <em>the force of air resistance against the object</em>. (choice-D)
Answer:
The gravitational force is related to the mass of each object.
The gravitational force is an attractive force.
Explanation:
Gravitational force is a long range force of attraction between any two masses.
Mathematically given as :
where:
are the masses
r= distance between the center of mass of the two objects.
G= gravitational constant = 
From the above relation of eq. (1) it is clear that,
Gravitational force is inversely proportional to the square of the distance and directly proportional to the masses.
The mass of an object is independent of its size due to the fact that density may vary for different objects.
The force of gravity varies with height as:
where:
gravity at height 
of the center of mass of the object from the center of mass of the earth.
and we know that force:
where: m= mass of the object.
