Newton's Laws: Understanding Force & Mass

In summary, when the rock is thrown upward with an initial speed of 15 m/s, the force on the ball is 2 N.
  • #1
Shay10825
338
0
Hi everyone! I need some help.

1.)A .2 kg rock is thrown upward with an initial speed 15 m/s. What is the force on the ball in N when it reaches its maximum height?

Would I use kinematics to find the max height then use F=ma? If so how?
The answer is 2

2.) A woman whose mass as the surface of the Earth is 52 kg dives off a 2 m board into a swimming pool. What is her mass in kg while she is in a freefall?

The answer is 52.

~Thanks
 
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  • #2
[itex]F_{net}=ma[/itex], as you know. What is the net force acting on the rock while it is in the air? Hint: the net force on the rock is constant throughout its trajectory, nelgecting friction.
 
  • #3
But how would you do this for the max height?
 
  • #4
Shay, for a minute forget your problem and answer this question : "What are the different forces that are acting on an object that is in the air, and not in contact with any other object ?"
 
  • #5
If I just do F=ma then I need the acceleration. How do I fond the acceleration and max height with only the velocity and mass?
 
  • #6
What is the definition of mass, and how does an object's mass change ?
 
  • #7
Gokul43201 said:
Shay, for a minute forget your problem and answer this question : "What are the different forces that are acting on an object that is in the air, and not in contact with any other object ?"

gravity is the only force
 
  • #8
Shay10825 said:
If I just do F=ma then I need the acceleration. How do I fond the acceleration and max height with only the velocity and mass?

Forget about this for now. You'll learn how to do this only after you understand the answer to my question.
 
  • #9
Gokul43201 said:
What is the definition of mass, and how does an object's mass change ?
Does it change when it is in freefall?
 
  • #10
Shay10825 said:


gravity is the only force

Correct. So would that not be the answer to the question ?

How do you calculate the force due to gravity ? Does it have another name ?
 
  • #11
Shay10825 said:

Does it change when it is in freefall?

Okay, I'll give you a definition, and you tell me whether or not the mass changes.

Definition : The mass is the amount of matter contained in an object, (sort of like the number of atoms/molecules in the object).
 
  • #12
Gokul43201 said:
Correct. So would that not be the answer to the question ?

How do you calculate the force due to gravity ? Does it have another name ?

Is it 9.8 m/s^2 ?
 
  • #13
Gokul43201 said:
Okay, I'll give you a definition, and you tell me whether or not the mass changes.

Definition : The mass is the amount of matter contained in an object, (sort of like the number of atoms/molecules in the object).

I think the mass does not change.
 
  • #14
Shay10825 said:


Is it 9.8 m/s^2 ?

That's the acceleration due to gravity, represented by the symbol 'g'.

The force due to gravity involves this g and the mass m. And there's a common name for it - begins with a "W". What is this name and formula for the force ?
 
  • #15
Shay10825 said:


I think the mass does not change.

Correct, you can change the mass only by removing or adding stuff to the object.
 
  • #16
Weight
Fg = mg
 
  • #17
Ohhhhhhhhh!

Fg = ma
Fg= (.2)(9.8)
Fg=1.96

BUt why did they say "when it reaches its maximum height" and why does it talk about the initial speed? Is this just to confuse me?
 
  • #18
OK now I understand why 52 is the answer to #2. Is what I did for #1 correct?
 
  • #19
Correct. It's a trick question. The whole thing about the velocity and the maximum height is a distraction. They have no relevance to the problem.
 
  • #20
Thanks :smile:
 

FAQ: Newton's Laws: Understanding Force & Mass

1. What are Newton's Laws of Motion?

Newton's Laws of Motion are three fundamental principles that describe the relationship between force, mass, and motion. They were developed by Sir Isaac Newton in the 17th century and are considered the foundation of classical mechanics.

2. What is the First Law of Motion?

The First Law of Motion, also known as the Law of Inertia, states that an object at rest will stay at rest and an object in motion will stay in motion with a constant velocity unless acted upon by an external force.

3. What is the Second Law of Motion?

The Second Law of Motion states that the acceleration of an object is directly proportional to the net force acting on the object and inversely proportional to its mass. This means that the more force applied to an object, the greater its acceleration will be, and the more mass an object has, the less it will accelerate.

4. What is the Third Law of Motion?

The Third Law of Motion, also known as the Law of Action and Reaction, states that for every action, there is an equal and opposite reaction. This means that when a force is applied to an object, the object will exert an equal and opposite force in the opposite direction.

5. How are Newton's Laws used in real life?

Newton's Laws are used in many aspects of daily life, from driving a car to playing sports. They help explain how objects move and interact with each other, and are essential in fields such as engineering and physics. For example, understanding the Second Law of Motion is crucial in designing and building structures that can withstand forces such as wind and earthquakes.

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