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# Forces question got me flustered! Watch

1. Right the question is;
a tug boat is used to pull a barge along a river at constant velocity.
the tug boat pulls on the barge with a force of 4.5kN.
the tug boat engine drives the tug boat forward with a force of 7 kN.
1. what is the drag force on the tug boat due to the water?
2. what is the drag force on the barge due to the water?

i was thinking, is 1. just 7kN because the forces are equal and opposite, and velocity is constant

and for 2. is it just 7- 4.5?
any help would be just gorgeous!
thank you all!
2. (Original post by nerdeehoohaa)
Right the question is;
a tug boat is used to pull a barge along a river at constant velocity.
the tug boat pulls on the barge with a force of 4.5kN.
the tug boat engine drives the tug boat forward with a force of 7 kN.
1. what is the drag force on the tug boat due to the water?
2. what is the drag force on the barge due to the water?

i was thinking, is 1. just 7kN because the forces are equal and opposite, and velocity is constant

and for 2. is it just 7- 4.5?
any help would be just gorgeous!
thank you all!
2. The forwards force on the barge is just 4.5kN (from the tug). As it has constant velocity, the drag force on from the water must be equal to this but opposite in direction. [No resultant force]
1. The force pulling backwards on the tug, from the barge, is also 4.5kN by Newton 3.
The resultant force force on the tug is also zero (constant velocity) so to balance the forces of 7kN forwards (its own engine) and 4.5kN backwards (from the barge) there must also be a force of 2.5kN backwards on it from the drag due to the water.
3. (Original post by Stonebridge)
2. The forwards force on the barge is just 4.5kN (from the tug). As it has constant velocity, the drag force on from the water must be equal to this but opposite in direction. [No resultant force]
1. The force pulling backwards on the tug, from the barge, is also 4.5kN by Newton 3.
The resultant force force on the tug is also zero (constant velocity) so to balance the forces of 7kN forwards (its own engine) and 4.5kN backwards (from the barge) there must also be a force of 2.5kN backwards on it from the drag due to the water.
Agreed.

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Updated: December 5, 2010
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