# Why is there no acceleration in the southern/y direction?

• yashboi123
yashboi123
Homework Statement
A river flows due south with a speed of 2.5 m/s. You steer a motorboat across the river; your velocity relative to the water is 5.2 m/s due east. The river is 650 m wide.

How far south of your starting point will you reach the opposite bank?
Relevant Equations
Δ x = v 0 t + 1 2 a t 2
v = v 0 + a t
Δ x/ Δt = v
The correct answer is obtained by rearranging Δ x/ Δt = v. However, I assumed there would be some acceleration in the y direction so I tried to use the kinematic equations. To find the time I simply rearranged Δ x/ Δt = v, assigning v=5.2 m/s and Δ x = 650. I assumed there is no acceleration in the x/east direction, but why is there no acceleration in the y/southern direction?

Think about what “velocity relative to the water” means.

so essentially relative to water means that speed is constant, in turn causing there to be no acceleration for the east direction. But why can we just assume the river has no acceleration?

yashboi123 said:
But why can we just assume the river has no acceleration?
Because the problem statement says that the river flows at a speed of 2.5m/s.
That implies an acceleration of 0.

Also, you're not given a value for acceleration, so if you aren't going to assume zero, what value would you assume?

I see, thank you.

DaveC426913 said:
Because the problem statement says that the river flows at a speed of 2.5m/s.
That implies an acceleration of 0.

Also, you're not given a value for acceleration, so if you aren't going to assume zero, what value would you assume?
Haha I thought we would have to find the acceleration ourselves then solve

Why do you keep saying "acceleration" ?

hmmm27 said:
Why do you keep saying "acceleration" ?
What else should I say.

yashboi123 said:
What else should I say.
Something relevant to the question, which has nothing that implies an acceleration.

That's why I asked the question

So, what do you see as implying the need for an "acceleration" ?

## Why is there no acceleration in the southern/y direction despite an applied force?

The absence of acceleration in the southern/y direction despite an applied force could be due to a counteracting force of equal magnitude in the opposite direction. This results in a net force of zero, leading to no acceleration.

## Could friction be the reason for no acceleration in the southern/y direction?

Yes, friction could be the reason. If the force applied in the southern/y direction is countered by an equal force of friction, the net force would be zero, resulting in no acceleration.

## How does Newton's First Law explain no acceleration in the southern/y direction?

Newton's First Law states that an object will remain at rest or in uniform motion unless acted upon by a net external force. If there is no net force in the southern/y direction, the object will not accelerate in that direction.

## Can the object's mass affect acceleration in the southern/y direction?

While the object's mass affects the magnitude of acceleration (according to Newton's Second Law, F = ma), if there is no net force in the southern/y direction, the mass is irrelevant to the lack of acceleration in that direction.

## Is it possible that the object is in equilibrium in the southern/y direction?

Yes, if the object is in equilibrium, the forces acting on it in the southern/y direction are balanced, resulting in no net force and hence no acceleration.

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