How to Calculate Velocity with Air Drag and Given Variables?

In summary, the person is trying to find the velocity of a car going downhill and has the final and initial velocities, as well as the energy lost and other variables such as the coefficient of drag and density of air. They are considering using the drag force equation to find the velocity, but are unsure how to incorporate it into the equation. They also mention finding the net sum of forces and using an equation to find t, but it is unclear what equation they are referring to.
  • #1
michelle2011
4
0

Homework Statement


I am trying to find the velocity of a car as it is going down hill. I have the final velocity which is 11.2 m/s and the initial velocity which is 2.23m/s. I have to include Air drag to get my velocity. I also know that there was 21,456 J of energy lost from up the hill to down the hill. I also know that the hill is 18 m long...Here are more variables that i was given
Coffiecient of drag: 0.38
Density of air: 1.293 kg/m^3
Cross-sectional are of car: 1.4 m by 1.6 m
Angle of hill: 10 degrees
Coefficient of rolling friction: 0.020


Homework Equations


The only thing I have to work with is the drag force equation.
F(D)=0.5pv^2C(D)A
p=Density of air
C(D)=coefficient of drag
A=cross-sectional area of the car
v=velocity of car

The Attempt at a Solution


I am contemplating on using that but velocity is involved in the equation and velocity is what I am looking for.
 
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  • #2
hi michelle2011! :smile:

total force = ma = mdv/dt

so what are the forces? :wink:
 
  • #3
What you want to do is find the net sum of forces acting on the car and then convert that to a velocity by using Tim's equation.
 
  • #4
Are my net forces rolling force and air drag??
 
  • #5
michelle2011 said:
Are my net forces rolling force and air drag??

net force is the (vector) sum of all the forces

(ie there is only one net force)

your three forces are the friction, the drag, and gravity
 
  • #6
In the equation you gave me can I just find my (t) from a simple equation??
 
  • #7
(just got up :zzz:)
michelle2011 said:
In the equation you gave me can I just find my (t) from a simple equation??

i'm confused … you're looking for v, not t :confused:

anyway, what equation do you get? :smile:
 

FAQ: How to Calculate Velocity with Air Drag and Given Variables?

1. What is air drag and how does it affect velocity?

Air drag, also known as air resistance, is the force exerted by air on an object moving through it. It acts in the opposite direction to the object's motion and increases with the object's velocity. This means that as an object moves faster, the air drag becomes greater, causing a decrease in velocity.

2. How is air drag calculated?

The air drag on an object can be calculated using the formula Fd = 1/2 * ρ * v^2 * Cd * A, where ρ is the density of air, v is the velocity of the object, Cd is the drag coefficient, and A is the cross-sectional area of the object.

3. How does the shape of an object affect air drag?

The shape of an object plays a significant role in determining the amount of air drag it experiences. Objects with a streamlined shape, such as a bullet, experience less air drag compared to objects with a large surface area, such as a parachute. This is because a streamlined shape allows air to flow smoothly around the object, while a larger surface area creates more turbulence and thus more air drag.

4. Can air drag be completely eliminated?

No, air drag cannot be completely eliminated. However, it can be minimized by reducing the object's velocity, changing its shape to be more streamlined, or using materials that reduce air drag, such as aerodynamic coatings.

5. How does air density affect air drag?

The density of air affects air drag by determining how much air molecules are present in a given volume. Objects moving through denser air will experience more air drag compared to objects moving through less dense air. This is why airplanes and cars have better performance at higher altitudes where the air density is lower.

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