Solving one-dimensional Motion Problems

In summary: This exercise is to help you understand the importance of those things and to give you practice in drawing diagrams and defining variables.In summary, the conversation is about a physics problem involving a car's acceleration while braking. The instructions ask for a pictorial representation of the situation, along with a coordinate system and defined symbols for known and unknown quantities. The conversation also discusses how to approach solving the problem and the importance of drawing diagrams and defining variables.
  • #1
43
0
I'm having a little trouble with the wording in this problem. (And this isn't the first time).
My instructions are:
"Draw a pictorial representation of each situation described below. That is, (i) sketch the situation, showing appropriate points in the motion, (ii) establish a coordinate system on your sketch, and (iii) define appropriate symbols for the known and unknown quantities. Do not solve.

a) A car traveling at 30m/s screeches to a halt, leaving a 55m long skid mark. What was the car's acceleration while braking?

So am I solving the cars acceleration or not? So far I've gotten my known as the velocity 30m/s, my unknowns would be displacement and acceleration, and a very rough picture of a car and an arrow showing forward motion with 30m/s under it and then a line indicating the 55m skid mark. I have no idea what it's really asking me to do though. Do I solve it? (It says not to be then asks a very specific question.) I'm so confused.
 
Physics news on Phys.org
  • #2
Welcome to Physics Forums :smile:

Sylis said:
I'm having a little trouble with the wording in this problem. (And this isn't the first time).
My instructions are:
"Draw a pictorial representation of each situation described below. That is, (i) sketch the situation, showing appropriate points in the motion, (ii) establish a coordinate system on your sketch, and (iii) define appropriate symbols for the known and unknown quantities. Do not solve.

a) A car traveling at 30m/s screeches to a halt, leaving a 55m long skid mark. What was the car's acceleration while braking?

So am I solving the cars acceleration or not?
Looks like you are not to actually solve the problem. Even though it proceeds to ask for the acceleration, which I agree is confusing. It sounds like your teacher (or professor) wants people to get practice with drawing sketches to set up a problem.

So far I've gotten my known as the velocity 30m/s, my unknowns would be displacement and acceleration, and a very rough picture of a car and an arrow showing forward motion with 30m/s under it and then a line indicating the 55m skid mark. I have no idea what it's really asking me to do though. Do I solve it? (It says not to be then asks a very specific question.) I'm so confused.
Well, I don't agree 100% with your knowns and unknowns. There are typically 5 quantities to worry about in a problem like this. Hopefully you are already familiar with them:
  • a the acceleration
  • vi the initial velocity (some people use u instead of vi)
  • vf the final velocity (some people just use v for this)
  • x the displacement (some people use s, some use Δx instead)
  • t the time
I recommend doing the following, when you are trying to solve a problem like this:

1. Look at every quantity given in the problem statement, and figure out where in the above list it belongs.

2. Look at what is being asked for in the question (acceleration, in this case). It should be in the above list. That is your unknown.

3. Make sure you have 3 knowns. Well, you might have 4. But you really need 3 in order to solve this type of problem***. If you don't have 3, you are probably missing a verbal clue in the problem statement that tells you one of the quantities is zero.

Regarding #1 above: Your problem statement has the values "30 m/s" and "55 m". You have incorrectly assigned "30 m/s" as "the velocity", without specifying if that is the initial or final velocity. Also, you have not figured out how the "55 m" is relevant. While it's possible that a problem statement might provide unneeded information, that is not the case here: the 55 m is needed -- or would be needed, if you were actually going to solve the problem.

Regarding #2: I agree that acceleration is an unknown.

*** Exception regarding #3: this does not apply when you have a constant-velocity problem. But it does apply here, since velocity is not constant.

Hope that helps.
 
  • #3
It very much did help thank you so much. I'm glad I found these forums lol.
 
  • #4
Basically it's just asking you to draw and label the diagram that you would use to help you solve the problem in (a) but you don't need to actually solve the problem.

It's because too many people rush to solve problems without drawing a suitable diagram and without defining the variables used in their equations.
 
  • #5


As a scientist, it is important to carefully read and understand the instructions provided in a problem. In this case, the instructions are asking you to draw a pictorial representation of the situation and establish a coordinate system, but not to solve the problem. This means that you should not calculate the acceleration of the car. Instead, you should focus on creating a visual representation of the situation and identifying the known and unknown quantities. This can help you better understand the problem and potentially lead to a more accurate solution when you do eventually solve it. It is important to follow instructions carefully in scientific work in order to accurately represent and solve problems. If you are still unsure about the instructions, it may be helpful to consult with a teacher or colleague for clarification.
 

1. What is one-dimensional motion?

One-dimensional motion refers to the movement of an object along a single straight line, usually represented by the x-axis in mathematics.

2. How do you solve one-dimensional motion problems?

To solve one-dimensional motion problems, you first need to identify the known and unknown variables, set up a coordinate system, and then use the appropriate equations of motion to solve for the unknown variable.

3. What are the equations of motion used in one-dimensional motion?

The three main equations of motion used in one-dimensional motion are the displacement equation (x = x0 + v0t + 1/2at2), the velocity equation (v = v0 + at), and the acceleration equation (v2 = v02 + 2a(x-x0)).

4. What is the difference between average velocity and instantaneous velocity?

Average velocity is the total displacement divided by the total time, while instantaneous velocity is the velocity at a specific moment in time. Average velocity gives a general idea of an object's motion over a period of time, while instantaneous velocity gives information about an object's motion at a specific point in time.

5. Can one-dimensional motion be represented graphically?

Yes, one-dimensional motion can be represented graphically with a position vs. time graph, a velocity vs. time graph, or an acceleration vs. time graph. These graphs can help visualize an object's motion and can be used to solve one-dimensional motion problems.

Suggested for: Solving one-dimensional Motion Problems

Back
Top