Answer:
Part a)

Part b)

Explanation:
Part a)
If block is sliding up then net force must be zero and friction will be in opposite to the direction of motion of the block


so we have





Part b)
If block is sliding down then net force must be zero and friction will be in opposite to the direction of motion of the block


so we have





Uhh it is used to detirmine heat
Answer:
The maximum safe depth in salt water is 3758.2 m.
Explanation:
Given that,
Diameter = 20 cm
Radius = 10 cm
Thickness = 9.0 cm
Force 
Inside pressure = 1.0 atm
We need to calculate the area
Using formula of area

Put the value into the formula


We need to calculate the pressure
Using formula of pressure

Put the value into the formula



We need to calculate the maximum depth
Using equation of pressure


Put the value into the formula


Hence, The maximum safe depth in salt water is 3758.2 m.
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