Help Needed: Solving Car Braking Problem w/Time Crunch

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SUMMARY

The discussion focuses on solving a physics problem involving a car with a mass of 1300 kg, initially traveling at 40 km/h, which comes to a stop over a distance of 15 m. Participants identify the need to calculate the magnitude of the stopping force and the time required for the speed change using kinematic equations. The relevant equations include \( v^2 = v_0^2 + 2a\Delta x \) for acceleration and stopping distance, and the relationship between force, mass, and acceleration for determining the stopping force. Additionally, the discussion explores how doubling the initial speed affects stopping distance and time.

PREREQUISITES
  • Understanding of Newton's second law of motion
  • Familiarity with kinematic equations
  • Basic knowledge of units of measurement (e.g., kg, m/s, m)
  • Ability to manipulate algebraic equations
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  • Learn how to apply Newton's second law to calculate force
  • Study kinematic equations in detail, focusing on acceleration and time
  • Explore the effects of changing initial conditions on motion parameters
  • Practice solving similar physics problems involving motion and forces
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Students studying physics, particularly those focusing on mechanics, as well as educators seeking to clarify concepts related to motion and forces.

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OK, I have some homework, due soon, and could use some help. If you can give me an answer and show me how you got it, great, but I'm here to learn too.
A car with a mass of 1300kg is initially moving at a speed of 40 km/h when the brakes are applied and the car is brought to a stop in 15 m. Assuming that the force that stops the car is constant, find (a) the magnitude of that force and (b) the time required for the change in speed. If the initial speed is doubled and the car experiences the same force during the braking, by what factors are (c) the stopping distance and (d) the stopping time multiplied?
So there are 4 parts to this problem. I'm here to learn, but I'm also crunched for time, so any help would be appreciated. :smile:
 
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physics newb said:
OK, I have some homework, due soon, and could use some help. If you can give me an answer and show me how you got it, great, but I'm here to learn too.
A car with a mass of 1300kg is initially moving at a speed of 40 km/h when the brakes are applied and the car is brought to a stop in 15 m. Assuming that the force that stops the car is constant, find (a) the magnitude of that force and (b) the time required for the change in speed. If the initial speed is doubled and the car experiences the same force during the braking, by what factors are (c) the stopping distance and (d) the stopping time multiplied?
So there are 4 parts to this problem. I'm here to learn, but I'm also crunched for time, so any help would be appreciated. :smile:

u have to tell us how you have tried to solve the problem yourself...
 
I haven't, I don't even know where to begin. That's why I'm here. Once I get started, things should start clicking. Does the mass of the car have anything to do with how long it will take to slow down?
 
Does anyone have an idea as to what the next step is?
 
For a) you need the acceleration, and you only know the initial and final velocities, and the distance, so you need an equation that only uses these variables. Do you know what it would be? Don't forget to multiply a by the mass to get the force. Then for b), you need the time, so since you have the acceleration, you can use another equation of motion, and solve it for time. For c) and d), go back and solve these 2 equations for x and t, with the new initial speed.
 
v^2 = v_0^2 + 2 a \Delta x
Would this be it?
 
Time is not my luxury here. What is the next thing I do?
 
What confuses you? Tomsk's post seems to clear it up pretty well. Your equation is the correct one to use for (a).
 

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