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A bookshelf is 2 m long, with supports at its ends (P and Q).
a)A book weighing 10 N is placed in the middle of the shelf. What are the upward forces at P and Q?
b)The book is moved so that it is 50 cm from Q. Use moments to calculate P the forces at P and Q.
c)The bookshelf weighs 10 N. Repeat parts b and taking into account
weight of the shelf as well as the weight of the book.

Respuesta :

Answer:

a) P + Q = 2 P = 10 N    P = Q = 5 N      each exerts the same force

b)  P x1 = Q x2      if x1 and x2 are not equal (torque about pivot point)

50 Q = 150 P  or Q = 3 P      balancing torques

Since P + Q = 10       Q = 7.5 N and P = 2.5 N

c) take torques about P

100 * 10 + 100 * 10 = 200 * Q    

Q = 10 N        P + Q = 20 N upward and the force on the fulcrum in the middle is 10 + 10 = 20 N down (10 N for shelf and 10 N for book)      

 

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