Check work on kinematics problem

In summary, the question is asking how long it takes for a truck to reach a speed of 100km/h from rest and the distance it travels in that time. The book states that it takes 148.5s and covers a distance of 1904m, while the student's calculations result in a time of 140.85s and a distance of 950.57m. The student shares their calculations and asks for someone to check their answers as the book has had mistakes before. The expert notes that the truck's acceleration rate is 17m/s^2 and provides a summary of the conversation.
  • #1
caperjay
6
0

Homework Statement


A truck accelerates uniformly from rest to 48km/h in 20s, holds speed for 2 minutes, and then accelerates to 100km/h at a rate of 17m/s^2. How long does it take, from rest, to reach 100km/h and what distance it traveled in this time?


The book says it takes 148.5s, and I keep getting 140.85s.
For distance the book says 1904m, and I been getting lower at 950.57m.

I was hoping someone could just check the answers for me, since I am doing a course from a book that has had a lot of mistakes thus far, if it turns out that my answers are wrong I will post my what I've been doing to get some help on it. Thanks much!
 
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  • #2
Hey Caperjay, could you post some work? Then we'll see what's up.
 
  • #3
mateomy said:
Hey Caperjay, could you post some work? Then we'll see what's up.

Heres what I've done. For the total time I got 20s + 120s + (13.33=27.78 + 17m/s^2xt) where t turns out to be 0.85s, for a total of 140.85s.

For total distance I've got (0+13.33)/2 x 20s + (13.33 + 13.33)/2 x 120s + (13.33 + 27.78)/2 x 0.85s, for a total of 950.57m.
 
  • #4
"at a rate of 17m/s^2"

Mighty powerful truck!
 
  • #5


As a scientist, it is important to always double check our work and make sure our calculations are accurate. In this problem, it seems like there may be a discrepancy between the book's answers and your own. I would recommend going back through your calculations and checking for any errors. It is also helpful to show your work and equations so that others can assist you in finding any mistakes.

In terms of the time and distance calculations, it would be helpful to know if you are using the correct units for acceleration (m/s^2 vs km/h^2). It is also important to consider any rounding errors that may have occurred during your calculations.

If you are still unable to find the error in your calculations, it may be helpful to consult with a classmate or instructor for additional assistance. It is always better to catch and correct any mistakes early on rather than continue with incorrect answers.

Overall, it is important to be diligent and thorough in your work as a scientist, and to always double check for accuracy and precision.
 

1. How do I know if my kinematics problem is correct?

To check if your kinematics problem is correct, you can use the equations of motion and plug in the given values to see if they produce the expected result. Additionally, you can use a kinematics calculator or online solver to verify your answer.

2. What are some common mistakes to watch out for when checking kinematics problems?

Some common mistakes to watch out for when checking kinematics problems include using the wrong units, forgetting to include acceleration due to gravity, and mixing up initial and final values. It is also important to double check your calculations to ensure they are correct.

3. How do I check if my kinematics problem is set up correctly?

To check if your kinematics problem is set up correctly, you can use the given information to create a diagram of the problem. This will help you visualize the motion and ensure that you have correctly identified the initial and final values, as well as the direction of motion.

4. Can I use kinematics equations to solve any type of motion problem?

Kinematics equations can be used to solve problems involving constant acceleration and constant velocity. However, they may not be applicable for more complex motion problems, such as those involving changing acceleration or non-uniform motion.

5. What should I do if my answer does not match the expected result?

If your answer does not match the expected result, double check your calculations and make sure you are using the correct equations and values. It may also be helpful to try solving the problem using a different method or asking for assistance from a classmate or teacher.

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