Friction Questions
1 Jo, Daniel and Helen are pulling a metal ring. Jo pulls with
a force of 100N in one direction and Daniel with a force
of 140 N in the opposite direction. If the ring does not
move, what force does Helen exert if she pulls in the same
direction as Jo?

Helen's force must be of 40 N in the same direction as Jo.

Explanation:

Net Force

When a number of forces are applied to an object, the net force is the sum of all the forces considered as vectors.

When all forces act on a straight line, only two possible directions are considered and they can be arbitrarily assigned positive and negative signs.

Jo pulls with a force of 100 N in a direction considered as positive (for example). Daniel applies a force of 140 N in the opposite direction, obviously negative. The net force of these two forces is 100 N - 140 N = - 40 N.

This means there is a resultant non-zero force in the direction of Daniel's. If we are told the net force is zero because of Helen's force, it must be applied in the same direction as Jo's force to balance.

Helen's force must be of 40 N in the same direction as Jo.

fgravity=10x10=100n case 1

fgravity=30x20=600n case 2

6 times more

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