Question

What is matter wave? What do you understand by in phase and out phase waves? Calculate the wavelength associated with a body of mass 1.5 kg moving witha velocity of 100 m s-1.

Answer 1

Matter waves or de Broglie waves are waves associated to any object having mass. They describe the wave nature of any matter. The wavelength of a matter wave is given by the equation
$\lambda=\frac{h}{mv}$
Where h is the planck's constant, m is the mass of the body and v is it's velocity.
For bigger day-to-day objects like football or a car (macroscopic objects - objects that can be seen with naked eye) they have a lot of mass so their wavelength is very small and the wave nature is negligible, that is why you don't see wave characters in day to day objects. The wave nature becomes more apparent in the microscopic level (on the level of elementary particles like electrons). The mass of an electron is very small so the wavelength becomes large, such that the wave nature can't be neglected, that is why fundamental particles are said to have dual nature - particle and wave nature.
You are given the values
$m=1.5 kg$
$v=100ms^{-1}$
and h is planck's constant whose value is given as
$h=6.626 \times 10^{-34} Js$
So just put in the values and find the answer !