Answer:
Yes , it is possible for two different atoms of carbon to have different numbers of neutrons in their nuclei .
Explanation:
Isotopes -
Atoms of the element with same number of the electrons and protons , but differ in the number of neutrons , are called as the isotopes .
The isotopes of the element have the same number of protons and electrons , hence have the same chemical and physical properties .
Many isotopes occurs naturally .
In case of Carbon ,
Carbon too have isotopes ,
i.e.
Carbon - 13 and Carbon - 14
carbon - 13 , have seven neutrons
Carbon - 14 , have eight neutrons .
Frictional force and Applied force has same “magnitude” and “opposite” direction.
Option: B
<u>Explanation</u>:
When a book is moved horizontally by applying “force” on the book, the frictional force is opposed to the book by the table. Here, this “frictional force” is opposing the book has the same force what we applied on the book but this frictional force and the applied force are opposite in direction. Always the “frictional force” is opposite to the “applied force” which stops the object to move. For example, if a force applied leftward to the object the frictional force is acted on the right side of the object.
When two objects are in contact they experience a "frictional force". This "frictional force" acts opposite to the force applied on to move the object.
Formula for "frictional force" is 
Where,
is coefficient of friction and N is normal force.
if i renember correctly its b
Consider the upward direction of motion as positive and downward direction of motion as negative.
a = acceleration due to gravity in downward direction = - 9.8 
v₀ = initial velocity of rock in upward direction = ?
v = final velocity of rock at the highest point = 0 
t = time to reach the maximum height = 4.2 sec
Using the kinematics equation
v = v₀ + a t
inserting the values
0 = v₀ + (- 9.8) (4.2)
v₀ = 41.2 