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The student in multiple-choice question3 then pulls the rubber band so that it is at the 9-in. mark. The block of wood slides faster and faster with a constant acceleration, and as it moves, the student moves his hand so that the rubber band is always pullet to the 9-in. mark. The net force on the block when the rubber band is stretched 9 in. is
(A) greater than (B) equal to
(C) less than (D) unrelated to the net force on the block when the rubber band was stretched 7 in.

Amit Saxena

11 Years agoGrade upto college level

1 Answer

Navjyot Kalra

11 Years ago

The correct option is (A) greater than.
The block of wood just starts to move when the rubber band reaches the 8-in. mark. Since the block of wood will not move in between the mark 5-inches to 8-inches, therefore the magnitude of applied force (F_app) on the block of wood is smaller than the frictional force (f).
Above 8 in mark, the block starts moving. This means there is a net force which acts in the direction of the applied force.
Thus, the net force acting on the block of wood (Fnet) is
F_net = F_app – f
or,
F_app = F_net + f
Therefore the net force on the block when the rubber band is stretched 9 in. is greater than the net force on the block when the rubber band is stretched 7 in.
From the above observation we conclude that, option (A) is correct.

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