Question

Will cars stop instantaneously if the car brakes are perfect?

Answer 1

Instantly means directly or immediately. Instantaneously means happening so soon (in reference to something else) that no delay is perceptible.

Complete step by step solution:
It is impossible to prevent the car if even the brakes are perfect because for a car to prevent during a zero interval , the deceleration required must be infinite, which isn't possible. No, it's impossible . so as to form velocity zero in an infinitesimally small interval of your time , the car needs an infinite acceleration which isn't possible.
To stop a car, the brakes need to obviate that K.E. they are doing so by using the force of friction to convert that K.E. into heat. Once you press your foot down on the pedal , a connected lever pushes a piston into the brake cylinder , which is crammed with hydraulic fluid.
When brakes are applied to a moving vehicle, the space it travels before stopping is named stopping distance. It's a crucial factor for road safety and depends on the initial velocity $v_0$ and therefore the braking capacity, or deceleration which is caused by the braking.

Note:
When a force is applied to the brakes of a vehicle, there's work done by the friction between the brakes and therefore the wheel. This reduces the K.E. of the vehicle, slowing it down and causing the temperature of the brakes to extend.