The correct answer is A, 2x^3 - x^2 +3x +7
This is an interesting (read tricky!) variation of Rydberg Eqn calculation.
Rydberg Eqn: 1/λ = R [1/n1^2 - 1/n2^2]
Where λ is the wavelength of the light; 1282.17 nm = 1282.17×10^-9 m
R is the Rydberg constant: R = 1.09737×10^7 m-1
n2 = 5 (emission)
Hence 1/(1282.17 ×10^-9) = 1.09737× 10^7 [1/n1^2 – 1/25^2]
Some rearranging and collecting up terms:
1 = (1282.17 ×10^-9) (1.09737× 10^7)[1/n2 -1/25]
1= 14.07[1/n^2 – 1/25]
1 =14.07/n^2 – (14.07/25)
14.07n^2 = 1 + 0.5628
n = √(14.07/1.5628) = 3
Hello
This is a problem of accelerated motion, where the acceleration involved is the gravitational acceleration:

, and where the negative sign means it points downwards, against the direction of the motion.
Therefore, we can use the following formula to solve the problem:

where

is the initial vertical velocity of the athlete,

is the vertical velocity of the athlete at the maximum height (and

at maximum height of an accelerated motion) and S is the distance covered between the initial and final moment (i.e., it is the maximum height). Re-arranging the equation, we get
Answer:
Force of friction is (-30 N).
Explanation:
The force applied on the box across the floor is 30 N.
The force of gravity is (-8 N) and the the normal force is 8 N.
It is based on Newton's third law of motion. Newton's third law of motion states that the force acting on object 1 to object 2 is equal in magnitude of the force from object 2 to 1 but in opposite direction.
Here there is force of 30 N is applied in horizontal direction. The frictional force act in opposite direction. So, the force of friction is -30 N so that box across the floor.