Answer:
Lithium
Explanation:
The equation for the photoelectric effect is

where
is the energy of the incident photon, with
h being the Planck constant
c is the speed of light
is the wavelength of the photon
is the work function of the metal (the minimum energy needed to extract the photoelectron from the metal)
is the maximum kinetic energy of the emitted photoelectrons
In this problem, we have
is the wavelength of the incident photon
is the maximum kinetic energy of the electrons
First of all we can find the energy of the incident photon

Converting into electronvolts,

So now we can re-arrange the equation of the photoelectric effect to find the work function of the metal

So the metal is most likely Lithium, which has a work function of 2.5 eV.
Normal is the other half of an action-reaction pair
If a person is sitting on a chair , there must be a gravitation force acting in downward direction which is equal to the weight of that person . That means the person is exerting a force on the chair equal to its weight . But the person is not falling down the chair , because of newtons third law of motion .
There must be a counter force which is equal and opposite to the force exerted by the person on the chair , in order to make net force equal to zero and to make that man in stationary state ( no movement ) .That force is called Normal force which is been acted by the chair on the person .This implies Normal is the other half of an action-reaction pair
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Answer:

Explanation:
Using the tension in the spring and the force of the tension can by describe by
T = kx
, T = mg
Therefore:

With two springs, let, T1 be the tension in each spring, x1 be the extension of each spring. The spring constant of each spring is 2k so:


Solve to x1





Answer:
k = 17043.5 N/m = 17.04 KN/m
Explanation:
First we need to find the force applied by safe pn the spring:
F = Weight of Safe
F = mg
where,
F = Force Applied by the safe on the spring = ?
m = mass of safe = 800 kg
g = 9.8 m/s²
Therefore,
F = (800 kg)(9.8 m/s²)
F = 7840 N
Now, using Hooke's Law:
F = kΔx
where,
K = Spring Constant = ?
Δx = compression = 46 cm = 0.46 m
Therefore,
7840 N = k (0.46 m)
k = 7840 N/0.46 m
<u>k = 17043.5 N/m = 17.04 KN/m</u>