Newton’s law of universal gravitation stars that every object in the universe attracts every other object
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Since the stone is being dropped, you know that it is in free fall. That means you can use your kinematics equations, since acceleration is free fall is a constant 9.8 m/s^2 down.
Looking through the kinematics equations, you want to use one that lets you find t, time, while using variables that we already know the values of. Notice that in the equation:
Say that the rock starts at point x=0. That means the initial value of x, the position, is
= 0m, and the final position is 
= -4.9m. We are also told that the initial velocity, 
= 0, assuming it's being dropped from rest, and a = -9.8 m/s^2. Plug these numbers in and solve for t:
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Answer: t = 1 s
Looking through the kinematics equations, you want to use one that lets you find t, time, while using variables that we already know the values of. Notice that in the equation:
Say that the rock starts at point x=0. That means the initial value of x, the position, is
-----
Answer: t = 1 s
First of all, we need to write the First Law of thermodynamics assigning the correct sign convention:
where
is the change in internal energy of the system
Q is the heat absorbed/released
W is the work done
and the signs are assigned based on whether there is an increase in the internal energy or not. Therefore:
Q is positive if it is absorbed by the system (because internal energy increases)
Q is negative if it is released by the system (because internal energy decreases)
W is negative if it is done by the system on the surrounding (because internal energy decreases)
W is positive if it is done by the surrounding on the system (because internal energy increases)
Using these definitions, we can now fill the text of the question:
When a system is heated, heat is ABSORBED by the system. The amount of heat added is given a POSITIVE sign. When a system is cooled, heat is RELEASED by the system. The amount of heat is given a NEGATIVE sign. If a gas expands, it must push the surrounding atmosphere away. Thus, work is done BY the system and is given a NEGATIVE sign. If a gas is compressed, then work is done ON the system. This work is given a POSITIVE sign.