# Thread: Help me solve this problem ive been having trouble.

1. ## Help me solve this problem ive been having trouble.

First Problem.

The Force needed to keep a car from skidding on a curve vasies directly as teh weight of the car and the square of the and inversely as the radius of the curve. It requiers 266lb of force to keep a 2200 lb car traveling at 30 mph from skidding on a curve of radius 500 ft. How much force is required to keep a 3000lb car traveling at 45 mph from skidding on a curve of radius 400 ft.

Ive been having trouble doing this problem. I know that the formula is F=kws2
r
the r goes under kws2

i need help solving this.

2. Originally Posted by Weezergames
First Problem.

The Force needed to keep a car from skidding on a curve vasies directly as teh weight of the car and the square of the and inversely as the radius of the curve. It requiers 266lb of force to keep a 2200 lb car traveling at 30 mph from skidding on a curve of radius 500 ft. How much force is required to keep a 3000lb car traveling at 45 mph from skidding on a curve of radius 400 ft.

Ive been having trouble doing this problem. I know that the formula is F=kws2
r
the r goes under kws2

i need help solving this.
Think about the facts you've been given.

F varies inversely with the curvature, r. F varies directly with the square of the speed, s. F varies directly with the weight of the car, w.

So your formula should look like this:

$\displaystyle F = K\frac{s^2 w}{r}$

Where k is a constant of proportionality. You need to find k, but luckily, you know that the force required to keep a 2200 lb car traveling at 30 mph from skidding on a curve of radius 500 ft is 266lb. So if you plug these into the equation, you can solve for k. Then you will have a relation. From there, just plug in the numbers from the problem you don't know F for, and solve for F.

3. Please review this other posting of the same exercise.

4. Whoa. You're going to have to rewrite this:

The Force needed to keep a car from skidding on a curve vasies directly as teh weight of the car and the square of the and inversely as the radius of the curve. It requiers 266lb of force to keep a 2200 lb car traveling at 30 mph from skidding on a curve of radius 500 ft. How much force is required to keep a 3000lb car traveling at 45 mph from skidding on a curve of radius 400 ft.
$\displaystyle F=\frac{kws^{2}}{r}$ yes? Then:

F is force.
k is a constant.
w is the weight of the car
s is velocity.

Yes? On the first part of the problem we know that:

F=226lb/ft (not just lb's)
w=2200lb
s=30m/hr (converted into ft/s)
r=500ft

What don't we know. We don't know "k". We can solve:

$\displaystyle 226(lb/ft)=\frac{k(2200lbs)(30*5280ft/s)^{2}}{500ft}$ for k yes? I kept the units so you can see how we got lb/ft.

Then it's simply a matter of placing k back into our original equation, and solving a new one.