Calculations in regards to a car coming to a stop, help is needed.

In summary, the equation gives me an answer of 13.72 meters for stopping distance if I use 40km/h as the initial speed.
  • #1
connormaphone
5
0
I have been given a physics assignment which requires that I go over the physics of why 40km/h is a better speed to be followed in a school zone rather than 50km/h. (must include calculations for stopping distances etc.)

I used the formula Vo ^ 2 / 2 x μ x g.
It should give me the stopping distance if I am correct, Vo being the inital velocity, μ the friction coefficient and g for gravity. I first tried using 40km/h for Vo, .7 for μ and 9.8 for g.

40^2/2x.7x9.8

I use this and end up with 116.61...kilometres, this is evidently wrong and I am not sure what I am doing wrong as it should come out to 20-30 metres.
Can somebody please help?
Thanks.
(P.S I am in grade 11, so go easy on me :frown:)
 
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  • #2
You forgot to convert km/hr into m/s. It is essential that units are consistent.
 
  • #3
Oh that gives me an answer of 13.72, I feel stupid now. Thanks for the help!
 
  • #4
connormaphone said:
Oh that gives me an answer of 13.72, I feel stupid now. Thanks for the help!
13.72 m? Show how you arrived at that answer.
 
  • #5
40000^2/2x.7x9.8
Just realized this is wrong as well. I don't even know.
 
  • #6
Actualy, just made it 11.1 m/s which does equal 40km/h, I put it into the equation and ended up with approximately 9 metres.
 
  • #7
connormaphone said:
Actualy, just made it 11.1 m/s which does equal 40km/h, I put it into the equation and ended up with approximately 9 metres.
Now, you're talking! Looks Good!:smile:
And welcome to PF!
 
  • #8
connormaphone said:
I have been given a physics assignment which requires that I go over the physics of why 40km/h is a better speed to be followed in a school zone rather than 50km/h. (must include calculations for stopping distances etc.)

I used the formula Vo ^ 2 / 2 x μ x g.
It should give me the stopping distance if I am correct, Vo being the inital velocity, μ the friction coefficient and g for gravity. I first tried using 40km/h for Vo, .7 for μ and 9.8 for g.

40^2/2x.7x9.8

I use this and end up with 116.61...kilometres, this is evidently wrong and I am not sure what I am doing wrong as it should come out to 20-30 metres.
Can somebody please help?
Thanks.
(P.S I am in grade 11, so go easy on me :frown:)

Your starting formula is incorrect. The μg should be in the denominator. That is the deceleration. The larger the deceleration, the shorter the stopping distance.

Chet
 
  • #9
It is in the denominator. Parentheses would help, but I think it is in proper PEMDAS, per my recollect.
 
  • #10
Got it, thanks for the help guys!
 

1. How do you calculate the stopping distance of a car?

The stopping distance of a car can be calculated using the formula: stopping distance = reaction distance + braking distance. The reaction distance is the distance traveled by the car during the driver's reaction time, while the braking distance is the distance traveled while the car is decelerating. Both of these distances can be affected by factors such as speed, road conditions, and the condition of the car's brakes.

2. How does the weight of a car affect its stopping distance?

The weight of a car can greatly affect its stopping distance. A heavier car will have a longer stopping distance due to increased momentum and kinetic energy. This means the car will require more force to slow down and come to a complete stop. On the other hand, a lighter car will have a shorter stopping distance as it requires less force to slow down.

3. What is the difference between stopping distance and braking distance?

Stopping distance is the total distance traveled by a car while coming to a complete stop, which includes both the reaction distance and the braking distance. On the other hand, braking distance is only the distance traveled while the car is decelerating due to the brakes being applied. This means that the stopping distance is always greater than the braking distance.

4. How does the speed of a car affect its stopping distance?

The speed of a car has a significant impact on its stopping distance. The faster a car is traveling, the longer the stopping distance will be. This is because a car traveling at a higher speed will have more kinetic energy, which means it will require more force to slow down and come to a complete stop. In other words, the higher the speed, the longer the reaction time and the longer the braking distance will be.

5. How can you reduce the stopping distance of a car?

There are several ways to reduce the stopping distance of a car. One way is to maintain a safe and appropriate speed while driving. This will give the driver more time to react and apply the brakes, resulting in a shorter reaction distance. Another way is to ensure the car's brakes are in good condition and properly maintained. This will allow the car to decelerate more efficiently, reducing the braking distance. Proper road conditions, such as dry and smooth roads, can also help reduce the stopping distance of a car.

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