"Pip install tensorflow" only installs version 1.14 – how to install version 2 (with eager mode enabled?)
You install the version you want with:

pip install tensorflow=={version you want}

for example:

pip install tensorflow==2.0.0-beta1

If you are working in Google Colab it's even simpler, just type:

%tensorflow_version 2.x
import tensorflow as tf


and it will automatically import the latest version of TensorFlow 2.

Eager mode is default in TensorFlow 2.x, therefore you don't need to manually activate it. As soon as you import it it's immediately available.