Physics HW kinematics and sig figs

In summary: Please use proper English.In summary, the problem involves an indestructible bullet being fired through a board with a given thickness and initial and final velocities. The goal is to find the total time the bullet is in contact with the board and the thickness of a board that would stop the bullet assuming the same acceleration. Equations of motion are used to solve for the acceleration and time, but further details and work are needed to solve the problem accurately.
  • #1
raho14
2
0

Homework Statement


An indestructible bullet 2.10cm long is fired straight through a board that is 11.7cm thick. The bullet strikes the board with a speed of 416m/s and emerges with a speed of 296m/s.

Homework Equations


What is the total time that the bullet is in contact with the board?
What thickness of board (calculated to 0.10cm) would it take to stop the bullet, assuming the bullet's acceleration is the same?

The Attempt at a Solution


i have tried it but its not right.
for the first one:
d=vinitialxt+0.5at^2 solve for t
for second one:
vfinal^2=vintial^2+2ad where v final would be zero.
Please help me out it would be sincerely appreciated
 
Last edited:
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  • #2
raho14 said:

Homework Statement


An indestructible bullet 2.10cm long is fired straight through a board that is 11.7cm thick. The bullet strikes the board with a speed of 416m/s and emerges with a speed of 296m/s.


Homework Equations


What is the total time that the bullet is in contact with the board?
What thickness of board (calculated to 0.10cm) would it take to stop the bullet, assuming the bullet's acceleration is the same?



The Attempt at a Solution


i have tried it but its not right

Well, how about posting your work? We can't tell what you've done if you won't share.
 
  • #3
I'm trying not to give away the entire problem by being too pointy in my questions.

Write down the equations of motion for the first case.

With those equations, can you solve for the acceleration and the time? Do you have to make any assumptions to do it? Hint: Can you work out the average velocity while in contact with the board? And then, so what?
 
  • #4
i did get the acceleration which was right but i keep getting the time wrong i mean i usually get this but its confusing when u do it ten times so can u just tell me
 
  • #5
raho14,

Welcome to Physics Forums.

It would help if you would show more of your work, including your calculations. This will allow helpers to better understand where you are having difficulties.

Also take note that text-speak such as "u" meaning "you" is not allowed here.
 

FAQ: Physics HW kinematics and sig figs

1. What is kinematics in physics?

Kinematics is the branch of physics that deals with the study of motion without considering the forces that cause it. It involves analyzing the position, velocity, and acceleration of an object in motion.

2. How do you calculate velocity?

Velocity is calculated by dividing the change in position (displacement) by the change in time. It is represented by the equation v = Δx/Δt, where v is velocity, Δx is the change in position, and Δt is the change in time. The units for velocity are meters per second (m/s).

3. What are significant figures (sig figs) in physics?

Significant figures, also known as sig figs, are used in physics to indicate the precision of a measurement. They are all the digits in a number that are known with certainty, plus one estimated digit. For example, in the number 12.345, there are 5 significant figures.

4. How do you round off numbers using sig figs?

When rounding off numbers using sig figs, start by identifying the last significant figure. If the digit to the right of the last significant figure is less than 5, then the last significant figure remains the same. If the digit is 5 or greater, then the last significant figure is increased by 1. All digits to the right of the last significant figure are then dropped. For example, rounding 12.345 to 3 significant figures would give us 12.3.

5. Why is it important to use sig figs in physics calculations?

Sig figs are important in physics calculations because they indicate the precision of the data. When performing calculations, the result should have the same number of significant figures as the measurement with the least number of significant figures. This ensures that the result is not more precise than the original data. It also helps to avoid errors and maintain accuracy in calculations.

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