Newton's Second Law - Net Force and Constant Acceleration

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Homework Help Overview

The problem involves a water skier being pulled to a speed of 12 meters/second over a distance of 25 meters, with a focus on determining the net force exerted on the skier under the assumption of constant acceleration. The subject area pertains to dynamics and Newton's Second Law.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the application of Newton's Second Law and the need to express acceleration in terms of distance and time. There are attempts to calculate the time taken to reach the final speed and questions about the calculations leading to that time. Some participants express confusion over the dimensions of the quantities involved and the correct interpretation of the problem.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem and questioning each other's calculations. Some guidance has been offered regarding the need for additional equations to relate acceleration, distance, and time. There is no explicit consensus on the calculations or the approach to finding the net force.

Contextual Notes

Participants are working under the constraints of the problem's parameters, including the assumption of constant acceleration and the need to derive time from the given distance and final speed. There is a noted confusion regarding the definitions and relationships between force, acceleration, and speed.

electronXguy419
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1. A 92 kg water skier floating in a lake is pulled from rest to a speed of 12 meters/second in a distance of 25 meters. What is the net force exerted on the skier, with the assumption that his acceleration is constant?2. Force = Mass x Acceleration3. As far as I know, from using the equation from #2, I did 92kg x 12m/s, and got 1.104k Newtons.
 
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Hello guy, welcome to PF :smile:

As far as I know is not far enough: if you compare the dimensions you'll see that you don't get Newtons (kgm/s2) this way, but kgm/s -- which is the dimension of momentum.

So you'll need some more equations to find something with the dimension of time to get this in order. How long does it take to cover 25 m with constant acceleration and then have a speed of 12 m/s ?
 
Hi!

If I want to solve a problem in Dynamics, the first thing I do is to write down Newton's Second Law. You stated it right: F = ma
The two things we do not know here are the force, which is the solution of the exercise, and the acceleration which we have to express in another way, because we have two other data we didn't use up: the change of speed and the distance. Try to think about the definition of the acceleration (change of velocity over unit of time). We need an equation that links the distance and the time in function of the acceleration.
 
BvU said:
How long does it take to cover 25 m with constant acceleration and then have a speed of 12 m/s ?

I got approximately 2.08 seconds.
 
2.08333 s is a result. What is the calculation that gave you that result ? Because I get something else...

Suppose you have found this t. Then how do you calculate the net force exerted on the poor skier ? (I mean an equation with variable names, not a numerical result)
 
BvU said:
2.08333 s is a result. What is the calculation that gave you that result ? Because I get something else...

Suppose you have found this t. Then how do you calculate the net force exerted on the poor skier ? (I mean an equation with variable names, not a numerical result)

In answer to the first question, I took the distance (25m) and divided it by the speed (12m/s); as for the second question: Fnet = F1 + F2.
 
The speed isn't 12 m/s ! It clearly says the skier is accelerated with a constant acceleration from rest to 12 m/s.
RE the equation: FNET is supposed to be the answer for the exercise, but what are F1 and F2 ?
 

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