Physics excercises

[Shadow]

Okay, I've got some exercises here that I need some help with. I tried to do them, but I always get to a point where I just don't know what to do...

 

1)

 

A train is sitting (idle) in front of a tunnel of the length [math]d=320m[/math] so that the trains front is placed exactly at the beginning of the tunnel. When a signal was given, the train started to move. In this instant a person standing at the very end of the train started counting the time. He noted that he entered the tunnel when his watch showed the time [math]t_1=30 s[/math] and exited the tunnel when his watch showed the time [math]t_3=50 s[/math]. The motion of the train was evenly accelerated the whole time.

 

What is the length [math]l[/math] of the train, and the time [math]t_2[/math] of the exit of the front of the train from the tunnel?

 

I think I could calculate both on my own, the problem is I don't know how to figure out the acceleration...

 

2) A pilots destination lied northward of his current position. He pointed his airplane north, but didn't take into consideration that a southwest wind was blowing. In [math]t_1=60 minutes[/math] he realized that his course had changed due to the wind. So he pointed the planes direct axis to the west and in [math]t_2= 15 minutes[/math] reached his destination. The velocity of the plane in windless conditions is [math]v_1=180 km/h[/math].

 

What is the distance [math]d[/math] between the starting point and the destination, and the velocity [math]v_2[/math] of the wind?

 

This I could solve if, again, I knew his velocity. But I don't know how to get to that. It's not that I'm lazy, I've tried...

 

 

 

I'd like to thank anyone and everyone for their help in advance. Please note that both the exercises are translated from Czech, so please excuse any grammatical errors that might appear. Also note that this isn't really homework. It's work that will decide my grade at the end of this semester....

[swansont]

Okay, I've got some exercises here that I need some help with. I tried to do them, but I always get to a point where I just don't know what to do...

 

1)

 

A train is sitting (idle) in front of a tunnel of the length [math]d=320m[/math] so that the trains front is placed exactly at the beginning of the tunnel. When a signal was given, the train started to move. In this instant a person standing at the very end of the train started counting the time. He noted that he entered the tunnel when his watch showed the time [math]t_1=30 s[/math] and exited the tunnel when his watch showed the time [math]t_3=50 s[/math]. The motion of the train was evenly accelerated the whole time.

 

What is the length [math]l[/math] of the train, and the time [math]t_2[/math] of the exit of the front of the train from the tunnel?

 

I think I could calculate both on my own, the problem is I don't know how to figure out the acceleration...

 

What equation do you have that will tell you your position, as a function of time, that includes acceleration in it?

 

 

2) A pilots destination lied northward of his current position. He pointed his airplane north, but didn't take into consideration that a southwest wind was blowing. In [math]t_1=60 minutes[/math] he realized that his course had changed due to the wind. So he pointed the planes direct axis to the west and in [math]t_2= 15 minutes[/math] reached his destination. The velocity of the plane in windless conditions is [math]v_1=180 km/h[/math].

 

What is the distance [math]d[/math] between the starting point and the destination, and the velocity [math]v_2[/math] of the wind?

 

This I could solve if, again, I knew his velocity. But I don't know how to get to that. It's not that I'm lazy, I've tried...

 

 

 

I'd like to thank anyone and everyone for their help in advance. Please note that both the exercises are translated from Czech, so please excuse any grammatical errors that might appear. Also note that this isn't really homework. It's work that will decide my grade at the end of this semester....

 

 

It's still necessary to get you to work it out, though, since it's schoolwork and it will affect your grade.

 

 

This is some vector addition. It should help to draw a diagram to set it up; it looks like the wind velocity is constant throughout, and that's one thing you need to find.

[NeonBlack]

When you say you don't know how to figure out the acceleration, do you mean you don't know the relevent equations, or you think you don't have enough information?

 

I find that it's usually the 2nd case, so what I normally suggest is to write down everything you know, even if you don't think it's important.

Keep Dr. Swanson's hint in mind and think about:

What are the positions of the front of the train and the back of the train at each of the given times?

How are the position of the front and back of the train related?

[Mr Skeptic]

A train is sitting (idle) in front of a tunnel of the length [math]d=320m[/math] so that the trains front is placed exactly at the beginning of the tunnel. When a signal was given, the train started to move. In this instant a person standing at the very end of the train started counting the time. He noted that he entered the tunnel when his watch showed the time [math]t_1=30 s[/math] and exited the tunnel when his watch showed the time [math]t_3=50 s[/math]. The motion of the train was evenly accelerated the whole time.

 

What is the length [math]l[/math] of the train, and the time [math]t_2[/math] of the exit of the front of the train from the tunnel?

 

I think I could calculate both on my own, the problem is I don't know how to figure out the acceleration...

 

You have two times, and one distance, and you know the acceleration is constant. To figure out the acceleration, you will want to know how fast the train was going when the person entered the tunnel. That's all I will say for now.