Two masses have a force F of magnitude 28.0N acting on them, as shown, through a

Question

Two masses have a force F of magnitude 28.0N acting on them, as shown, through a distance of 5.00m. The masses are mA =5.50kg and mB= 8.50 kg. The initials peed of the blocks is 1.50 m/s
a) Suppose they at first move on a frictionless plane. What is the approximate speed of block B after the force has been removed (after reaching 5.00m)?
b) The two masses both have the same coefficient of kinetic friction,uk=0.30. Suppose they now move on a rough plane. Compare the accelerations of block A and block B.

Explanation / Answer

F = ma >>> a = F/m = 28.0/8.5 = 3.294 m/s2

Vf2 - Vi2 = 2*a*x   >>>>> Vf2 = 2*a*x + Vi2 = 2*3.294*5 + 1.5^2  

 Vf= 5.93 m/s

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b)
F = ma    >>>>>  F- *m*g = ma

for block A:

28.0 - 0.30*5.50*9.8 = 5.50 * a   >>>>>   aA = 2.151 m/s2

for block B:

28.0 - 0.30*8.5*9.8 = 8.5 * a   >>>>>   aB = 0.354 m/s2

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c)
W = Fd

for block A:

W = F * d = 28 * 5 =  140 J

for block B:

W = F * d = 28 * 5 =  140 J

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d)

W = fd

for block A:

W = 0.30*5.50*9.8 * 5 = 80.85 J

for block B:

W = 0.30*8.5*9.8 * 5 =  124.95J

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e)
mechanical energy is conserved when there is no friction

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