Dynamics (Newtons Laws of Motion) and Projectile motions

In summary, the problem involves finding the time it takes for an 18kg rock under water to fall 1.0m with a frictional buoyancy of 129N. The acceleration of the rock is found to be 47.4 (units unclear). The next step would be to use a kinematic relationship to find the net force and use the second equation of motion to solve for the time.
  • #1
jelzap
4
0

Homework Statement


An 18kg rock is released under water.
The fricitional Buyoyance add up to 129N
How long will it take to fall 1.0m


Homework Equations





The Attempt at a Solution

 
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  • #2
jelzap said:

Homework Statement


An 18kg rock is released under water.
The fricitional Buyoyance add up to 129N
How long will it take to fall 1.0m


Homework Equations



You should have something here!

The Attempt at a Solution



... and here.
Hi jelzap.

What have you tried? Where are you stuck?
 
  • #3
well, i found the acceleration of the rock, i need to know what to do from there

M(A)=Fnety
M(A)= Fa+ Ff
M(a)=-(18*9.8) + 129N
18a=(-176.4)+129
a=47.4 (what are the units here?)

What do i do from here?
 
  • #4
jelzap said:
well, i found the acceleration of the rock, i need to know what to do from there

M(A)=Fnety
M(A)= Fa+ Ff
M(a)=-(18*9.8) + 129N
18a=(-176.4)+129
a=47.4 (what are the units here?)

What do i do from here?

You have: 18a=(-176.4)+129, which gives →  (18kg)a = (-47.4N).

How do you get a = 47.4?   What happened to the 18?   What happened to the "−" sign?

1 Newton = 1 kg·m/s2.   What units for Newton/kg ??

Look for a kinematic relationship involving: distance, (constant) acceleration, and time.
 
  • #5
Draw the FBD and find net force acting on the rock
equate it to manet (you can predict the direction pretty easily)

Find anet

now use second eqn of motion
 
Last edited:

1. What are Newton's Laws of Motion?

Newton's Laws of Motion are a set of three physical laws that describe the relationship between an object's motion and the forces acting on it. The first law states that an object at rest will remain at rest and an object in motion will remain in motion at a constant velocity unless acted upon by an external force. The second law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The third law states that every action has an equal and opposite reaction.

2. What is the difference between static and dynamic friction?

Static friction is the force that prevents two surfaces from sliding past each other when there is no relative motion between them. It is typically greater than dynamic friction, which is the force that resists the motion of two surfaces that are already in contact and sliding past each other.

3. How is projectile motion affected by air resistance?

Air resistance, also known as drag, can affect the trajectory of a projectile by slowing it down due to the force exerted by the air molecules on the object. This results in a curved path, known as a parabola, rather than a straight line. The amount of air resistance depends on the speed, size, and shape of the projectile.

4. What is the difference between speed and velocity?

Speed is a measure of how fast an object is moving, while velocity is a measure of both speed and direction. This means that an object can have a constant speed but varying velocity if its direction of motion changes. Velocity is a vector quantity, while speed is a scalar quantity.

5. How does mass affect an object's motion?

Mass is a measure of the amount of matter in an object. According to Newton's Second Law, the greater the mass of an object, the more force is needed to accelerate it. This means that an object with a larger mass will have a slower acceleration compared to an object with a smaller mass when acted upon by the same force.

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