Water boiling is an example of a physical change. The rest are chemical changes.
Hope that helps!!
The electron is accelerated through a potential difference of

, so the kinetic energy gained by the electron is equal to its variation of electrical potential energy:

where
m is the electron mass
v is the final speed of the electron
e is the electron charge

is the potential difference
Re-arranging this equation, we can find the speed of the electron before entering the magnetic field:

Now the electron enters the magnetic field. The Lorentz force provides the centripetal force that keeps the electron in circular orbit:

where B is the intensity of the magnetic field and r is the orbital radius. Since the radius is r=25 cm=0.25 m, we can re-arrange this equation to find B:
Answer:
Speed of the car 1 =
Speed of the car 2 =
Explanation:
Given:
Mass of the car 1 , M₁ = Twice the mass of car 2(M₂)
mathematically,
M₁ = 2M₂
Kinetic Energy of the car 1 = Half the kinetic energy of the car 2
KE₁ = 0.5 KE₂
Now, the kinetic energy for a body is given as

where,
m = mass of the body
v = velocity of the body
thus,

or

or

or

or

or
.................(1)
also,

or

or

or

or

or

or

or

or

and, from equation (1)

Hence,
Speed of car 1 =
Speed of car 2 =