Answer: X
Explanation:
This situation can be illustrated as a car in circular motion (image attached).
In circular motion the acceleration vector
is always directed toward the center of the circumference (that's why it's called centripetal acceleration).
So, in this case the arrow labeled X is the only that points toward the center, hence it represents the car's centripetal acceleration
Answer: 0.016 h
Explanation:

It is given that, biker has an average speed = 18 km/h
Total distance traveled = 0.30 km
Therefore, time taken by biker to travel this distance:

Thus, the biker takes 0.016 hours to travel the segment of 0.30 km at an average speed of 18 km/h.
Answer:
Relative population is 2.94 x 10⁻¹⁰.
Explanation:
Let N₁ and N₂ be the number of atoms at ground and first excited state of helium respectively and E₁ and E₂ be the ground and first excited state energy of helium respectively.
The ratio of population of atoms as a function of energy and temperature is known as Boltzmann Equation. The equation is:
= 
= 
Here g₁ and g₂ be the degeneracy at two levels, K is Boltzmann constant and T is equilibrium temperature.
Put 1 for g₁, 3 for g₂, -19.82 ev for (E₁ - E₂) and 8.6x10⁵ ev/K for K and 10000 k for T in the above equation.
= 
= 3.4 x 10⁹
= 2.94 x 10⁻¹⁰
Answer:
Diameter of the cylinder will be 
Explanation:
We have given young's modulus of steel
Change in length 
Length of rod 
Load F = 11100 KN
Strain is given by 
We know that young's modulus 
So 

We know that stress 
So 

So 