Answer:
<em>The acceleration of the racecar is</em> 
Explanation:
<u>Uniformly Accelerated Motion</u>
It's a type of motion in which the velocity of an object changes by an equal amount in every equal period of time.
Following the definition above, the acceleration is defined as:

Where a is the constant acceleration, vo the initial speed, vf the final speed, and t the time.
The racecar goes from vo=18.5 m/s to vf=46.1 m/s in t=2.47 seconds, thus the acceleration is:



The acceleration of the racecar is 
Explanation:
Iron has tiny magnetic domains inside it. Each domain acts like a tiny magnet with its own magnetic field. These domains are randomly distributed thus resulting in zero magnetic field and iron doesn't behave like a magnet.
When a copper wire is wound around the nail and current is passed through the coil, magnetic field is generated. This magnetic field penetrates through the nail. Due to this the magnetic domains of the nail align in the same direction thus having a net magnetic field. The nail behaves like a magnet till the time current flows through the coil.
Answer:
All molecules of one substance are identical (exactly the same)(2)
Calculated weight (by experimentally) of Earth is 5.972 × 10²⁴ N
Hope this helps!