Well, first of all, EVERY physical quantity is measured in a combination
of 2 or more units, except for mass, length, time, and electric charge.
ALL other units are made out of these. So it should not surprise you.
[ Example: Speed = (length) / (time) ]
Density is not the mass of a substance. It's the mass of a substance in
a standard volume of it. So the density is made of the mass in any lump
and the volume of that lump. That way, no matter how much of a substance
you have, you can always compare the lump you have to all other substances.
The aluminum foil would reflect the most light !
Answer:
The smallest radius will be four (4) times the initial radius
Explanation:
The car maintains a constant angular speed. According to Newton's Second Law F = m a
1. 
2. 
Replacing 2 in 1
3. 
Where:
Fr= Frictional force
Rp= Initial Radius
An= Centripetal Acceleration
M= Mass
V= Velocity
Also we have that:
4. 
μ= Coefficient of friction between the car and the surface
M= Mass
W= Weight
G= Gravity
r is cleared from equation 3
5. 
Replacing 4 in 5
6. 
Simplifying
7. 
Now we have a new velocity equal to twice the initial velocity, We replace it by 2v in equation 7
8. 
Computing
9. 
Replacing 5 in 9

It is transferred evenly to water through air
120/60= 2m per s
220/55= 4m per s
720/80= 9m per s
Fastest run: 3rd run
Speed: 9m per s
Slowest: 1st run
Speed: 2m per s