As a demonstration, a physics teacher attaches a 7.5kg object to the ceiling by

Question

As a demonstration, a physics teacher attaches a 7.5kg object to the ceiling by a nearly massless string. This object then supports a 2.5kg object below it by another piece of string. Finally, another piece of string hangs off the bottom of the lower object to be pulled with ever increasing force until the string breaks somewhere. The string will break when the tension reaches 156 N.
a. Which length of the string will break first?
b. What is the maximum downward force the physics teacher can apply before the string breaks.

PLEASEE EXPLAINN!!!

Explanation / Answer

the tension in the upper string is more then the tension in the lower string

T = (m1 + m2)g,

while in lower string

T' = m2g

hence the upper string breaks first.

Tmax = 156N

Tmax - (m1 + m2)g = F(max)

156 - (7.5 + 2.5)9.8 = F

F = 58N

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