Solving Hard Physics Problems: Tips and Strategies for Acing Your Homework

[Legend05]

Well I am doing my homework and there are a few problems that are so hard that i can't even try to get an answer... Hoping you can give me tips to get started,
Here they are:

1) A world-class sprinter accelerates to his maximum speed in 3.9 s. He then maintains this speed for the remainder of a 100m race, finishing with a total time of 8.9 s.

What is his average acceleration during the first 3.9s?


2) The engineer of a passenger train traveling at 25.0 m/s sights a freight train whose caboose is 200m ahead on the same track. The freight train is traveling at 15.0m/s in the same direction as the passenger train. The engineer of the passenger train immediately applies the brakes, causing a constant acceleration of -0.100 m/s^2, while the freight train continues with constant speed. Take x=0 at the location of the front of the passenger train when the engineer applies the brakes.


Where will the colision take place? (i've already determined that there will be one)



3)two stunt drivers drive directly toward each other. At time t=0 the two cars are a distance D apart, car 1 is at rest, and car 2 is moving to the left with speed v0. Car 1 begins to move at t=0, speeding up with a constant acceleration ax. Car 2 continues to move with a constant velocity.

At what time do the two cars collide?

Find the speed of car 1 just before it collides with car 2.




So, i tryed my best but it seems like it's missing data.. maybe the teacher did a mistake. =S
Any tips and feedback is appreciated.
Thx

 

[JaredJames]

Hi, please can you show your own attempts as per PF guidelines. Once done, I will gladly assist you.

There is nothing missing from the questions. All are answerable with given data.

Jared

 

[Legend05]

1 and 3 i didnt even try anything because idk where to start. none of the formulas i got work.

#2 i found that after 200m the speed of the train is 24.2 m/s with v^2x=vx0^2+2ax(x-x0). Doesnt help much.

im missing time and postion..how am i supposed do do something without these 2.

 

[JaredJames]

Well let's start with 2 then seeing as you have a start at it.

You know the deceleration, initial speed and final speed.

Using v = u + at, calculate the time it takes to reach 15m/s from 25m/s (after 15m/s no collision can occur).

Once you have the time, using s = ut + 0.5at^2 you can calculate the distance traveled by the passenger train in the deceleration time.

Using s = 0.5(u + v)t you can then work out the distance traveled by the freight train (don't forget to add the 200m separation).

From that you can work out where the collision will occur.

v = final speed, u = initial speed, a = acceleration, t = time, s = distance

 

[rwisz]

I understand the frustration of encountering difficult physics problems. However, it is important to remember that these challenges are what help us grow and develop our problem-solving skills. Here are some tips and strategies that can help you tackle these problems with confidence.

1) Start by understanding the problem: Before attempting to solve a physics problem, make sure you have a clear understanding of what is being asked. Read the problem statement carefully and identify the given information and what is being asked for.

2) Draw a diagram: A visual representation of the problem can often provide valuable insights and help you organize your thoughts. This is especially helpful for problems involving motion, forces, and collisions.

3) Use appropriate equations: Make sure you are familiar with the relevant equations and principles for the problem at hand. Write down the equations that you will need and make sure you understand how to use them.

4) Break it down: If a problem seems overwhelming, try breaking it down into smaller, more manageable parts. This can help you focus on one aspect at a time and make the problem more approachable.

5) Practice, practice, practice: Solving physics problems requires practice and familiarity with the concepts and equations. The more you practice, the more comfortable you will become with different types of problems.

6) Seek help when needed: Don't be afraid to ask for help if you are stuck on a problem. Consult your textbook, classmates, or your teacher for clarification and guidance.

In regards to the specific problems you mentioned, here are some additional tips:

1) For the first problem, use the equation a = (vf - vi)/t to calculate the average acceleration during the first 3.9 seconds. Remember to convert the units to be consistent (e.g. m/s^2).

2) For the second problem, you can use the equations d = vit + 1/2at^2 and v = vi + at to determine the position and velocity of the passenger train at the time of collision. Remember to use the negative acceleration for the passenger train due to the brakes.

3) For the third problem, you can use the equations d = vit + 1/2at^2 and v = vi + at to solve for the time and velocity of car 1 at the time of collision. Remember to consider the direction of motion for each car.

Remember, don't get discouraged if you are struggling with these problems. Keep practicing and seeking help when needed, and