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- Homework Statement
- An airboat with mass 3.50 3 102 kg, including the passenger,

has an engine that produces a net horizontal force of 7.70 3 102 N,

after accounting for forces of resistance (see Fig. 4.7). (a) Find the acceleration

of the airboat. (b) Starting from rest, how long does it take the

airboat to reach a speed of 12.0 m/s? (c) After reaching that speed, the

pilot turns off the engine and drifts to a stop over a distance of 50.0 m.

Find the resistance force, assuming it’s constant.

- Relevant Equations
- Newton's 2nd law of motion

regarding the last question.

I know that resistance is a negative force because it goes in the opposite direction to the movement of the boat. So whenever, I want to apply Newton's 2nd law of motion: the sum of forces = m a

I should write - F resit = m.a.

However, they have considered the resistance a positive force in this exercise. Why?

I know that resistance is a negative force because it goes in the opposite direction to the movement of the boat. So whenever, I want to apply Newton's 2nd law of motion: the sum of forces = m a

I should write - F resit = m.a.

However, they have considered the resistance a positive force in this exercise. Why?