force does the floor exert on the block- (b) A rope is tied to the block and is

Question

force does the floor exert on the block- (b) A rope is tied to the block and is run vertically over a pulley The other end is attached to a free-hanging 10.0.1b object What now is the force exerted by the floor on the 15.0.1b block? (c) If the 10.0 1b object in part (b) is replaced with 20.0.1b object, what is the force exerted by the floor on the 15.0-1b block? To meet a U.S. Postal Service requirement, employees footwear must have a coefficient of static friction of 0,500 or more on a specified tile surface. A typical athletic shoe has a coefficient of 0,800. In an emergency, what is the minimum time interval in which a person starting from race can move 5,00 m on the tile surface if she is wearing (a) footwear meeting a Postal Service minimum and (b) a typical athletic shoe?

Explanation / Answer

The simple logic that is used in solving the problem is that 'the maximum friction force limits the maximum acceleration one can have without slipping.'
g =9.8m/s^2
Now  
Maximum friction force available = Mg

Ma= Mg => a = g

a) = .5

=> a = 4.9m/s^2

Now using the formula s= ut +.5at^2 we have s= 5 u =0 t =? a =4.9

5 = .5*4.9*t^2

=> t = 1.43 sec

b)  = .8

=> a = 7.84m/s^2

Now using the formula s= ut +.5at^2 we have s= 5 u =0 t =? a =7.84

5 = .5*7.84*t^2

=> t = 1.13 sec

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