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Yuri [45]
3 years ago
10

A classroom which normally contains 26 people is to be air- conditioned. A person in the classroom typically dissipates heat at

a rate of 360 kJ/h. The room is lit with 15 light bulbs which each consume 40 W. A 200 W fan also operates in the room near a door to a computer closet. This fan pulls warm air into the classroom under the door at a rate of 200 kg/h. The room gains 10 kJ in energy (enthalpy) for each kg of warm air which enters. The air comes under the door at 10 m/s and leaves the room with negligible velocity through a large vent 3 m above the floor. Otherwise the room is well sealed. Finally, the room gains 5,000 kJ/h by heat transfer through the walls and windows. Determine the air-conditioner capacity, in kW, that is needed to keep the room at a steady temperature. Are any terms of the energy balance negligible?
Engineering
1 answer:
lutik1710 [3]3 years ago
7 0

Answer:

Explanation:

Heat dissipated by 26 people per second

= 26 x 360 x 1000 / (60 x 60)

= 2600 J

Heat dissipated by bulbs per second

= 15 x 40

= 600 J

Heat dissipated by fans per second

200 J

Heat dissipated by air coming in

= 200 x 10 x 1000 / (60 x 60)

=555.55 J

Heat gain by walls

= 5000 x 1000 / (60 x 60)

= 1388.88 J

Total heat gain per second

= 2600 + 600+200+555.55

= 3955.55 J

Capacity of air-conditioner required

= 3955.55 J/s

= 3.9 kJ/s

= 3.9kW

= 4 kW

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1. The system must be able to manage multiple students (max of 15) and their grades for assignments from three different assignm
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Answer:

#include<iostream>

#include<string.h>

using namespace std;

class gradebook;

class student

{

friend class gradebook;

char name[20]; // std name

int homework_grades[6], quiz_grades[6], exam_grades[4]; //grades array

float homework_avg, quiz_avg, exam_avg, final_avg;

};

class gradebook

{

student list[16];

public:

char gb_name[20]; // gradebook name

int max, total;

// Constructor

gradebook()

{

strcpy(gb_name,"noname");

max = 5;

total = 0;

for(int i=1;i<=15;i++)

{

strcpy(list[i].name,"noname");

for(int j=1;j<=5;j++)

{

list[i].homework_grades[j] = -1;

list[i].quiz_grades[j] = -1;

}

list[i].exam_grades[1] = list[i].exam_grades[2] = list[i].exam_grades[3] = -1;

}

}

// Member functions

void display_std_name();

void display_grades(int, int);

int add_std(char *new_name);

int remove(int);

//int ch_grade(int, int);

};

// Define all functions

// Remove a student from list and adjust remaining

int gradebook::remove(int std_id)

{

if(total==0 || std_id>total || std_id<=0)

return 0;

if(std_id==total)

{

cout<<"\n“"<<list[std_id].name<<"” has been successfully removed! (New class size: 2)";

strcpy(list[total--].name,"noname");

return 1;

}

cout<<"\n“"<<list[std_id].name<<"” has been successfully removed! (New class size: 2)";

for(int i=std_id; i<total; i++)

{

list[i]=list[i+1];

}

total--;

return 1;

}

// Add student to gradebook

int gradebook::add_std(char *new_name)

{

if(total<15)

{

strcpy(list[++total].name, new_name);

return 1;

}

return 0;

}

// Display student name list

void gradebook::display_std_name()

{

for(int i=1;i<=total;i++)

{

cout<<"\n"<<i<<" "<<list[i].name;

}

}

/* Display grades of students

// (grade_id, student_number_in_list)

homework(1), quiz(2), exam(3)

*/

void gradebook::display_grades(int g_id, int std_id)

{

int i;

if(std_id<=total)

{

if(g_id==1)

{

for(i=1;i<6;i++)

{

cout<<"\n"<<i<<". ";

if(list[std_id].homework_grades[i]==-1) cout<<"<ungraded>";

}

}

else if(g_id==2)

{

for(i=1;i<6;i++)

{

cout<<"\n"<<i<<". ";

if(list[std_id].quiz_grades[i]==-1) cout<<"<ungraded>";

}

}

else if(g_id==3)

{

for(i=1;i<4;i++)

{

cout<<"\n"<<i<<". ";

if(list[std_id].exam_grades[i]==-1) cout<<"<ungraded>";

}

}

}

else

cout<<"\nNo such std exists";

}

/****************************** MAIN ****************************/

int main()

{

int main_choice, grade_choice, std_id, new_grade;

char g_name[20], s_name[20];

float a,b,c;

gradebook g;

do

{

cout<<"\n\n-=| MAIN MENU |=-";

cout<<"\n1. Add a student\n2. Remove a student\n3. Change a student’s grade\n4. Change group weights\n5. Change the gradebook name\n6. Display class averages\n7. Display full report\n0. QUIT\n";

cout<<"\nEnter an action: ";

cin>>main_choice;

switch(main_choice)

{

case 0:

break;

case 1:

cout<<"\n-=| ADDING STUDENT |=-";

cout<<"\nPlease enter the student’s name: ";

cin>>s_name;

if(g.add_std(s_name))

cout<<"\n"<<s_name<<" was successfully added to the gradebook!";

else

cout<<"\nStudents cannot be added because the gradebook is full!";

break;

case 2:

cout<<"\n-=| REMOVING STUDENT |=-";

if(g.total!=0)

{

g.display_std_name();

cout<<"\n Enter student to remove: ";

cin>>std_id;

if(!g.remove(std_id))

cout<<"\nCannot remove students";

}

else

cout<<"\nStudents cannot be added because the gradebook is full!";

break;

case 3:

cout<<"\n-=| CHANGING GRADE |=-\n1. Change a homework grade\n2. Change a quiz grade\n3. Change an exam grade";

cout<<"\nWhat type of grade would you like to change: ";

cin>>grade_choice;

g.display_std_name();

cout<<"\nWhich student’s grade would you like to change? ";

cin>>std_id;

//ch_grade(grade_choice, std_id);

g.display_grades(grade_choice, std_id);

break;

/*

case 4:

cout<<"\n-=| CHANGING WEIGHTS |=-";

while(1)

{

cout<<"\nEnter the weights, separated by spaces, in the order of homework, quizzes, and exams (total must add up to 1.0):";

cin>>a>>b>>c;

if(a+b+c==1.00)

break;

else

cout<<"\n Weights do not add up to 1.0, try again...";

}

break;

case 5:

cout<<"\n-=| CHANGING NAME |=-\nPlease enter the new name for the gradebook: ";

cin>>g_name;

cout<<"\n Gradebook name changed from “ ” to "<<g_name;

break;

case 6:

cout<<"\n-=| CLASS AVERAGES |=-";

cout<<"\nHomework average of class: ";

cout<<"\nQuiz average of class: ";

cout<<"\nExam average of class: ";

cout<<"\nFinal average of class: ";

break;

case 7:

break;

*/

default:

cout<<"\n\nInvalid input\n\n";

}

}while(main_choice!=0);

return 0;

}

Explanation:

6 0
3 years ago
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