6 The water surface in a deep well is 78.0 m below the top of the well. A person at the top of thewell drops a heavy stone down the well.Air resistance is negligible. The speed of sound in the air is 330 m s –1.What is the time interval between the person dropping the stone and hearing it hitting the water?A 3.75 s B 3.99 s C 4.19 s D 4.22 s7 Which statement is not a requirement of a pair of forces that obey Newton’s third law of motion?A The forces act in opposite directions.B The forces act on different objects.C The forces act on objects in contact.D The forces are of equal magnitude.

The problem can be divided into two parts: the time it takes for the stone to fall into the well and the time it takes for the sound of the stone hitting the water to reach the person.

1. Time for the stone to fall: We can use the equation of motion, d = ut + 0.5gt^2, where d is the distance, u is the initial velocity, g is the acceleration due to gravity, and t is the time. The stone is dropped, so u = 0. The distance d = 78.0 m and g = 9.8 m/s^2. Substituting these values, we get 78 = 0.59.8t^2. Solving for t, we get t = sqrt(78/4.9) = 4.0 s.

2. Time for the sound to reach the person: The speed of sound in air is given as 330 m/s. The time it takes for the sound to travel up the well is the distance divided by the speed of sound, t = d/v = 78/330 = 0.236 s.

Adding these two times together, the total time from when the stone is dropped until the person hears it hit the water is 4.0 s + 0.236 s = 4.236 s. So, the closest answer is D, 4.22 s.

For the second question, Newton's third law states that for every action, there is an equal and opposite reaction. This means that the forces are equal in magnitude and opposite in direction (A), and they act on different objects (B). However, the objects do not need to be in contact (C). So, the statement that does not meet the requirements of Newton's third law is C.