A 4.00-kg block rests between the floor and a 3.00-kg block as shown in the figu

Question

A 4.00-kg block rests between the floor and a 3.00-kg block as shown in the figure below. The 3.00-kg block is tied to a wall by a horizontal rope. If the coefficient of static friction is 0.800 between each pair of surfaces in contact, what force must be applied horizontally to the 4.00-kg block to make it move Two people, one of mass 85 kg and the other of mass 65 kg, sit in a rowboat of mass 90 kg. With the boat initially at rest, the two people, who have been sitting at opposite ends of the boat, 3.5 m apart from each other, now exchange seats. How far will the boat move

Explanation / Answer

6. Friction coefficient = 0.8

g = acceleration due to gravity = 9.8 m/s2

Force = 0.8*3*9.8 + 0.8*(3+4)*9.8 = 78.4 N

7.Since there is no external force so the center of mass of the system will be at the same point as initial

M1 = 85 kg at left side

M2 = 65 kg at right side

Mass of boat = 90 kg

Length of boat = 3.5 m

Initial center of mass about left corner = (90*1.75 + 65*3.5 )/(85+90+65)

= 1.604 m from left side

Let the boat move a distance X in left direction after position exchange

Final center of mass about left corner = (90*1.75 + 85*3.5 )/(85+90+65)

or X + 1.604 = 1.896

or X = 0.292 m Left side

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