没有找到类Laravel5

Class Book was not found. I have read the documentation that everything should work with namespaces , i have tried many different combinations but nothing works. help pls.

this is my code from routes.php

Route::get('/', function () 
{
    $book= new Book;
    $book->write='Mark Twain';
    $book->title='the adventures of ton saywer';
    $book->description='A nover about a young boy';
    $book->published=date('y-m-d');
    $book->save();

    return $book->id;
    return View::make('hello');
});

and this is my code from Book.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Book extends Model
{
    //
}

Try this code for creating new Book object

$book= new App\Book;