Answer
D. The acceleration vector of the planet points towards the center of the circle.
Explanation
For planetary motion , the velocity vector is always in a direction that is tangential to the direction of motion, not towards the center. Even though the speed of the planet may stay constant, it's velocity changes because it is constantly changing it's direction.
The centripetal force, which in this case is the force of gravity always points in the direction of the the center. The acceleration vector always points in the direction of the of the center of the circle just like the centripetal force.
Answer:

Explanation:
We knwo that Kirchoff law

where

hence

C is given as 0.04\times 10^{6} F
L= 1 H , so we have

the characteristic equation of this differential equation is


Therefore differential equation is

we know initial value if capacitor is given as 
Therefore


if no inital current is present then we hvae I(0) = Q'(0) = 0

therefre

hence charge is

Answer:

Explanation:
Centripetal acceleration (a) is defined as the square of an object's velocity (V^2) divided by the distance of the object from it's point/axis of revolution (r). So:

which allows us to solve for the velocity:

Graphite is great lubricant because each carbon atom forms weak covalent bonds with three other carbon atoms.
Diamond and graphite both are entirely made up of carbon but both the elements are completely different because of the bonding of carbon atoms. In graphite the carbon atoms form weak covalent with the other three carbon atom due to which there is less or no force between the atoms, and makes the graphite very soft and slippery, and graphite act as lubricant.