One dimensional motion problems.

[picklepie159]

Homework Statement

Hi, Physics Forum!
I have three problems. Since I am having a physics final on Tuesday, I am very nervous that I don't get these. These all concern one-dimensional motion.

1.) A plane is landing on the runway. It stops after 1100 meters, with an initial velocity of 110 meters. The mass is 4000 kilograms. Find A, time, and the coefficient of friction.

2.) A truck enters a highway at velocity of 10 m/s. It must accelerate to 25 m/s in 30 secs. Find the displacement and the acceleration. Now imagine that the flow of traffic is coming behind the truck at 20 m/s. How far away must the truck be not to crash into the traffic?

3.) A police car is at rest when a group of robbers pass them at 35 m/s. The officer starts accelerating when the crooks are at 500 m away. He must catch up to them within 30 seconds. What is the acceleration and displacement covered by the cop?

Homework Equations

I can't really type equations, So I basically know all of the one dimensional motion equations.
(I think). I'm sorry if you view this as lazy, but I am pretty tired right now and might pass out on the computer. Sorry.

The Attempt at a Solution

For number 1, I got the acceleration as -5.5 m/s squared. The time is 20 seconds. Now I am not sure about the mu. Net force is 22000 N, But I can't find anything else (ie. Applied force) to get Mu.

2.) I got the acceleration as 0.5 m/s squared. I then used the displacement forumula, to get d= 525 meters. I don't understand what equation I could use to find the distance from the traffic to the truck.

3.) I got the acceleration as 1.1 m/s squared. Besides that, I am totally lost. I know there is a policy that I have to try to solve my questions first, bit this is way beyond me. You don't have to give me the answers- a small nudge or clue towards it would be greatly appreciated.

Thanks for answering!

 

[tiny-tim]

hi picklepie159!

For number 1, I got the acceleration as -5.5 m/s squared. The time is 20 seconds. Now I am not sure about the mu. Net force is 22000 N, But I can't find anything else (ie. Applied force) to get Mu.

that's fine so far!

now use F = ma and F = µN

2.) I got the acceleration as 0.5 m/s squared. I then used the displacement forumula, to get d= 525 meters. I don't understand what equation I could use to find the distance from the traffic to the truck.

now you need to write two equations, one for the truck, and one for "the traffic", both to meet at the same place (but different displacements of course, and the same time t)

(same for question 3)