Enable and disable lightning input field based on checkbox?

Can you try below below to hide lightning:input fileds.

Lightning Component Code:
<aura:component implements="flexipage:availableForAllPageTypes" access="global" >
  <aura:attribute name="acc" type="Account" default="{ 'sobjectType': 'Account' }"/>
    <aura:attribute name="hide" type="string" default="true"/> 
    <form>
        <lightning:input name="Name" label="Name" aura:id="accountName" value="{!v.acc.Name}" onchange="{!c.disableFields}"/> 
        <aura:if isTrue="{!v.hide}"> 
            <lightning:input name="First Name" label="First Name" value="{!v.acc.firstName}"/>
            <Lightning:input name="Last Name" label="Last Name" value="{!v.acc.lastName}"/>
       </aura:if>   
    </form>
</aura:component>

js.cotroller Code
({
	disableFields : function(component, event, helper) {
        var val = component.find("accountName").get("v.value");
        if(val != null){
             component.set('v.hide' , "false");
        }
	}
})

Let me know if it didnt work for you.