Question

A cord is used to vertically lower an initially stationary block of mass m kg at a constant downward acceleration of g/4. the block has fallen a distance
d. (use any variable or symbol stated above as necessary.) (a) find the work done by the cord's force on the block. wf = 3mgd 4​ incorrect: your answer is incorrect. (b) find the work done by the weight of the block. wg = (c) find the kinetic energy of the block. k = (d) find the speed of the block. v =

Answer 1

(a) We know that work is the product of Force and Distance so: (in this case Distance is negative since going down so –d)

work = force * distance

work = M * (g - g/4) * -d

work = -3Mgd/4 

(b) The work by the weight of the block is simply:

work = Mgd 

(c) The kinetic energy is simply equivalent to the net work, therefore:

KE = net work

KE = Mgd/4 

(d) The velocity is:

v = √(2*KE/M)

Plugging in the value of KE from c:

v = √(2*Mgd / 4M)

v = √(gd / 2)