Newton's Second Law - Net Force and Constant Acceleration

In summary, the conversation discusses a problem involving a 92 kg water skier being pulled from rest to a speed of 12 meters/second in a distance of 25 meters. The equation Force = Mass x Acceleration is mentioned, along with the need for additional equations to find the solution. The participants also discuss the definition of acceleration and how to calculate the net force exerted on the skier.
  • #1
electronXguy419
3
0
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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  • #2
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 ?
 
  • #3
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.
 
  • #4
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.
 
  • #5
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)
 
  • #6
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.
 
  • #7
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 ?
 

FAQ: Newton's Second Law - Net Force and Constant Acceleration

1. What is Newton's Second Law?

Newton's Second Law states that the acceleration of an object is directly proportional to the net force acting on the object and inversely proportional to its mass. In other words, the greater the force acting on an object, the greater its acceleration will be. This law is expressed mathematically as F=ma, where F is the net force, m is the mass, and a is the acceleration.

2. What is net force?

Net force is the sum of all forces acting on an object. If there is more than one force acting on an object, the net force is calculated by adding or subtracting the individual forces depending on their direction. If the net force is zero, the object will either remain at rest or continue moving at a constant velocity.

3. How does net force affect acceleration?

According to Newton's Second Law, the acceleration of an object is directly proportional to the net force acting on it. This means that if the net force increases, the acceleration will also increase. Conversely, if the net force decreases, the acceleration will also decrease.

4. What is constant acceleration?

Constant acceleration is when an object's acceleration remains the same over time. This can occur when the net force acting on the object is constant, as in the case of objects falling under the influence of gravity. In these cases, the object's velocity will change by the same amount in each unit of time.

5. How is Newton's Second Law used in real life?

Newtons's Second Law has numerous applications in everyday life, such as in the design of cars, airplanes, and other vehicles. It is also used in sports, such as calculating the force needed to hit a baseball or kick a soccer ball. Additionally, it is used in engineering to design structures that can withstand the forces acting on them, and in medicine to understand the forces acting on the body during physical activities.

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