A heavy steel ball S is suspended by a string from a block of wood W, as
shown in the sketch. The entire system is dropped from a height.
Neglecting air resistance, the tension in the string is equal to
A zero
B the weight of S
C the difference of the masses of S and W
D the difference of the weights of S and W
if they are both free fall, zero tension.
To solve this problem, let's analyze the forces acting on the system.
When the system is dropped from a height, the only forces acting on it are the weight force of the ball and the wood.
The weight force is the force due to gravity acting on an object, given by the equation Fg = mg, where m is the mass of the object and g is the acceleration due to gravity.
In this case, the weight force of the ball is equal to its mass (mS) multiplied by the acceleration due to gravity (g), so FgS = mS * g.
Similarly, the weight force of the wood is equal to its mass (mW) multiplied by the acceleration due to gravity (g), so FgW = mW * g.
Now, when the system is at rest, the tension in the string must balance the weight forces of both the ball and the wood. Since the tension in the string is the only force acting in the upward direction, it should be equal to the difference between the weight forces of the ball and the wood.
Therefore, the tension in the string is equal to the difference of the weights of the ball and the wood, which is option D in this case.