Question

A certain type of string will break if the tension in the string exceeds 300 N. A number of 8-kg weights are hung one below the other from a hook in the ceiling using this string. When and how will the string break?

Answer 1

It is necessary to determine the number of minima weighs that makes the spring break. Consider that the weight of each block is:

w = m·g = (8 kg)(9.8 m/s²) = 78.4 N

then, consider that for n blocks, the total tension in the top string is equal to the total weight of the n blocks, given by:

W = 78.4n

then, if 300N is the capability of each string, if you equal 300 to the total weight of the n blocks, you can find the maximum number of blocks the first string can support, as follow:

78.4n = 300 divide by 78.4 both sides

n = 300/78.4

n = 3.83

Then, if you put 4 blocks the total weight of the blocks exceeds the capacbility of the string and it will break.

Hence, when the 4th weigh is added, the top spring segment will break.