Which has a greater momentum, a car or a bike moving at the same speed

Two friends at different locations want to communicate with each other by sending low energy signals. which of the following methods can they use to communicate? a) produce x-rays using colliding electrons and send them to radios, which capture sound b) send messages using infrared radiation, which travel in the form of waves c) send radio waves through intervening media like radio and television d) produce sound waves using microwaves from heated objects

Which metal exist in liquid state and can be cut with knife ?

What happens to isotopes that are unstable?