[SalesForce] Batch Apex Anonymous execution

Why am I not able to execute this batch class? I copied it from trail head tutorial,

Batch Class

   global class UpdateContactAddresses implements 
    Database.Batchable<sObject>, Database.Stateful {

    // instance member to retain state across transactions
    global Integer recordsProcessed = 0;

    global Database.QueryLocator start(Database.BatchableContext bc) {
        system.debug('Start Called');
        return Database.getQueryLocator(
            'SELECT ID, BillingStreet, BillingCity, BillingState, ' +
            'BillingPostalCode, (SELECT ID, MailingStreet, MailingCity, ' +
            'MailingState, MailingPostalCode FROM Contacts) FROM Account ' + 
            'Where BillingCountry = \'USA\''
        );
    }

    global void execute(Database.BatchableContext bc, List<Account> scope){
        system.debug('Execute Called');
        // process each batch of records
        List<Contact> contacts = new List<Contact>();
        for (Account account : scope) {
            for (Contact contact : account.contacts) {
                contact.MailingStreet = account.BillingStreet;
                contact.MailingCity = account.BillingCity;
                contact.MailingState = account.BillingState;
                contact.MailingPostalCode = account.BillingPostalCode;
                // add contact to list to be updated
                contacts.add(contact);
                // increment the instance member counter
                recordsProcessed = recordsProcessed + 1;
            }
        }
        update contacts;
    }    

    global void finish(Database.BatchableContext bc){
        system.debug('Finish Called');
        System.debug(recordsProcessed + ' records processed. Shazam!');
        AsyncApexJob job = [SELECT Id, Status, NumberOfErrors, 
            JobItemsProcessed,
            TotalJobItems, CreatedBy.Email
            FROM AsyncApexJob
            WHERE Id = :bc.getJobId()];
        // call some utility to send email
       // EmailUtils.sendMessage(a, recordsProcessed);
    }    

}

Execute code

UpdateContactAddresses obj = new UpdateContactAddresses(); 
Id batchId = Database.executeBatch(obj,100);

After it finish executing, I don't see any of my debug statements. Please help me understand why?