How Do You Calculate Skier's Mass and Acceleration with Newton's Second Law?

In summary, the skier has an acceleration of 5 m/s^2 during braking and the mass of the skier is 80 kg. It is important to be consistent with signs when using the equation F=ma.
  • #1
Nanu Nana
95
5

Homework Statement


A skier glides down a slope, and has at the bottom of the slope, at the beginning of a horizontal piece, a velocity of 30 m / s. He begins to brake and after 4 seconds later has a speed of 10 m / s. The friction between the skis and the snow is 400 N during braking.
a. What is the acceleration of the skier during braking?
b) What is the mass of the skier??

Homework Equations


F= m x a
vf=af x t + v(i) [/B]

The Attempt at a Solution


10m/s= af x 4s + 30m/s
af = -5m/s^2
Thats what i thought answer would be but answer should be +5m/s^2
Why is that ?
And for mass F= m x a
m = F/a
m = 400N / (-5)
m=-80 kg
Maybe I have to exchange value for v (initial ) and v (final )??[/B]
 
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  • #2
Nanu Nana said:
10m/s= af x 4s + 30m/s
af = -5m/s^2
Thats what i thought answer would be but answer should be +5m/s^2
Why is that ?
Your answer is perfectly fine. The minus sign means that the skier is slowing down. The magnitude of the acceleration is just 5 m/s^2; that's probably what they wanted for the answer.

Nanu Nana said:
And for mass F= m x a
m = F/a
m = 400N / (-5)
m=-80 kg
Realize that F and a point in the same direction and thus must have the same sign.

If you use a = -5 m/s^2, then you must use F = -400 N. (But you can just make them both positive, since they are in the same direction.)

The main thing is to be consistent with signs.
 
  • #3
Doc Al said:
Your answer is perfectly fine. The minus sign means that the skier is slowing down. The magnitude of the acceleration is just 5 m/s^2; that's probably what they wanted for the answer.Realize that F and a point in the same direction and thus must have the same sign.

If you use a = -5 m/s^2, then you must use F = -400 N. (But you can just make them both positive, since they are in the same direction.)

The main thing is to be consistent with signs.
Now i understand . Thank you very much
 

FAQ: How Do You Calculate Skier's Mass and Acceleration with Newton's Second Law?

1. What is the second law of Newton?

The second law of Newton, also known as the law of force and acceleration, states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

2. How is the second law of Newton represented mathematically?

The second law of Newton can be represented as F = ma, where F represents the net force, m represents the mass of the object, and a represents the acceleration.

3. What is the significance of the second law of Newton?

The second law of Newton is significant because it explains the relationship between force, mass, and acceleration. It also allows us to calculate the acceleration of an object when the net force acting on it is known.

4. Can the second law of Newton be applied to all types of motion?

Yes, the second law of Newton applies to all types of motion, including linear, circular, and rotational motion. It also applies to both stationary and moving objects.

5. How does the second law of Newton relate to the first law of motion?

The second law of Newton builds upon the first law of motion by stating that an object will only remain in a state of constant motion if the net force acting on it is zero. If there is a net force, the object will accelerate in the direction of the force.

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