You wish to boil 1.9 kg of water, which has a specific heat capacity of 4186 j/kg-k. the water is initially at room temperature (293 k). water boils at 373 k.
1) how much energy must be added to the water by heating it in order for it to start boiling?

6.36 105 J

Explanation:

In calorimetry all the energy given to a system is converted to heat and the equation for heat is

     Q = m   ΔT

The temperature can be in degrees Celsius or Kelvin since the interval between them is the same, substitute and calculate

Q = 1.9 4186 (373-293)  

Q = 6.36 105 J  

This heat equals the energy supplied

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.