Repeat Prob. 6/64, only now the 27-kg concrete block begins to move down the 20

Question

Repeat Prob. 6/64, only now the 27-kg concrete block begins to move down the 20 incline as shown. All other conditions remain as in Prob. 6/64.

6/64: The coefficient of static friction for both wedge sur- faces is 0.40 and that between the 27-kg concrete block and the 20 incline is 0.70. Determine the minimum value of the force P required to begin moving the block up the incline. Neglect the weight of the wedge.

Repeat Prob. 6/64, only now the 27-kg concrete block begins to move down the 20degree incline as shown. All other conditions remain as in Prob. 6/64. Problem 6/65 The coefficient of static friction for both wedge surfaces is 0.40 and that between the 27-kg concrete block and the 20 degree incline is 0.70. Determine the minimum value of the force P required to begin moving the block up the incline. Neglect the weight of the wedge. Problem 6/64

Explanation / Answer

the force acting on the block is

F = u_s x m x g x sinA

where u_s = 0.70,m = 27 kg,g = 9.8 m/s^2 and A = 20o

the work done is

W = F x S

where S is length of incline

we know that

W = K = (1/2)mv^2

where v is speed of block before coming to rest

or (1/2)mv^2 = F x S

or v = (2F x S/m)^1/2

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