hdu 1155 Bungee Jumping

http://acm.hdu.edu.cn/showproblem.php?pid=1155

Bungee Jumping

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 811    Accepted Submission(s): 349

Problem Description

Once again, James Bond is fleeing from some evil people who want to see him dead. Fortunately, he has left a bungee rope on a nearby highway bridge which he can use to escape from his enemies. His plan is to attach one end of the rope to the bridge, the other end of the rope to his body and jump off the bridge. At the moment he reaches the ground, he will cut the rope, jump into his car and be gone.

Unfortunately, he had not had enough time to calculate whether the bungee rope has the right length, so it is not clear at all what is going to happen when he jumps off the bridge. There are three possible scenarios: 
The rope is too short (or too strong), and James Bond will never reach the ground. 
The rope is too long (or too weak), and James Bond will be going too fast when he touches the ground. Even for a special agent, this can be very dangerous. You may assume that if he collides at a speed of more than 10 m/s, he will not survive the impact. 
The rope's length and strength are good. James Bond touches the ground at a comfortable speed and can escape. 
As his employer, you would like to know whether James Bond survives or whether you should place a job ad for the soon-to-be vacant position in the local newspaper. Your physicists claim that: 
The force with which James is pulled towards the earth is 
9.81 * w, 
where w is his weight in kilograms and 9.81 is the Earth acceleration in meters over squared seconds. 
Mr. Bond falls freely until the rope tautens. Then the force with which the bungee rope pulls him back into the sky depends on the current length of the rope and is 
k * Δl, 
where Δl is the difference between the rope's current length and its nominal, unexpanded length, and k is a rope-specific constant. 
Given the rope's strength k, the nominal length of the rope l in meters, the height of the bridge s in meters, and James Bond's body weight w, you have to determine what is going to happen to our hero. For all your calculations, you may assume that James Bond is a point at the end of the rope and the rope has no mass. You may further assume that k, l, s, and w are non-negative and that s < 200.

The input contains several test cases, one test case per line. Each test case consists of four floating-point numbers (k, l, s, and w) that describe the situation. Depending on what is going to happen, your program must print "Stuck in the air.", "Killed by the impact.", or "James Bond survives.". Input is terminated by a line containing four 0s, this line should not be processed.

 

Sample Input

350 20 30 75

375 20 30 75

400 20 30 75

425 20 30 75

450 20 30 75

400 20 30 50

400 20 30 80

400 20 30 85

0 0 0 0

 

Sample Output

Killed by the impact.

James Bond survives.

James Bond survives.

James Bond survives.

Stuck in the air.

Stuck in the air.

James Bond survives.

Killed by the impact.

 

一道很纯粹的物理分析题

 

1.如果绳长l >= 桥高s，那么重力势能全部转化为动能wgh = 1/2*w*v^2,

求出到达地面的速度v，如果v > 10,则 Killed by the impact.

否则能存活James Bond survives.

2.如果绳长l < s,则找绳的最大形变量，当绳到达最大长度l2时，重力势能全部转化为弹性势能wgh = 1/2*k*l1^2,

绳子的最大长度l2=本身长度l+形变量l1，如果绳的最大长度l2<s,则人在半空中Stuck in the air.

否则重力势能转化为动能和弹性势能（此时绳的形变量 = （s - l））wgh = 1/2*k*(s - l)^2 + 1/2*w*v^2,

求出到地面的速度v,如果v>10，则Killed by the impact.

否则能存活James Bond survives.

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>

#define g 9.81

using namespace std;

int main()
{
    double k, l, s, w;
    while(scanf("%lf%lf%lf%lf", &k, &l, &s, &w), k + l + s + w)
    {
        if(l >= s)
        {
            double v = sqrt( * g * s);
            if(v > )
                printf("Killed by the impact.\n");
            else
                printf("James Bond survives.\n");
            continue;
        }
        else
        {
            double l1 = sqrt(1.0 *  * w * g * s / k);
            if(l + l1 < s)
                printf("Stuck in the air.\n");
            else
            {
                double v = sqrt(1.0 * ( * w * g * s - k * (s - l) * (s - l)) / w);
                if(v > )
                    printf("Killed by the impact.\n");
                else
                    printf("James Bond survives.\n");
            }
        }
    }
    return ;
}