Answer:
A. elements of the same kind with different numbers of neutrons
Explanation:
As we know that an atom is represented by

here we know that
z = atomic number
A = atomic number + number of neutrons
now if the number of neutrons in an atom is different but having same number atomic number then the combination of such group of atoms is known as isotopes.
So here we have

so above is the example of isotopes
Answer:
A point on the outside rim will travel 157.2 meters during 30 seconds of rotation.
Explanation:
We can find the distance with the following equation since the acceleration is cero (the disk rotates at a constant rate):

Where:
v: is the tangential speed of the disk
t: is the time = 30 s
The tangential speed can be found as follows:

Where:
ω: is the angular speed = 100 rpm
r: is the radius = 50 cm = 0.50 m
Now, the distance traveled by the disk is:

Therefore, a point on the outside rim will travel 157.2 meters during 30 seconds of rotation.
I hope it helps you!
The fluid that is being passed through the syringe and needle is incompressible, which means that it will transmit pressure equally. Therefore, the pressure on the plunger will be equivalent to the pressure on the needle. We also know that:
Pressure = Force / Area
Pressure on plunger = 4 / (π*(0.012/2)²)
Pressure on plunger = 35.4 kPa
Pressure on needle = 35.4 kPa
35.4 kPa = F / (4 / (π*(0.0025/2)²)
F = 0.17 N
The force on the needle is 0.17 N
<u>Note that</u>:
The gravitational potential energy = 
where m: is the mass, g: the acceleration due to the gravity and h is the height from the earth surface
Then, we can increase the gravitational potential energy by increasing the mass or the height from the earth surface
<u>In our question</u>, we can increase the gravitational potential energy by
<u>A) Strap a boulder to the car so that it wights more.</u>