Answer:
the correct answer is D.) 2,4
From Literature:
The amount of energy in the photons is given by this equation:
E = hf
where E = energy
h = Planck's constant = 6.63 * 10^-34 Joule seconds
f = frequency of the light, Hz
Given:
E= 3.00 eV and Planck's constant
To solve for the frequency, E = 3.00 eV
1 electronvolt = 1.60218 x 10^-19 Joules
3 * 1.60218 x 10^-19 Joules = 6.63 * 10^-34 Joule seconds * f
f = 7.25 x 10^14 /second or hertz
Therefore, the threshold frequency of the material is 7.25 x 10^14 Hertz.
Answer:

Explanation:
Given:
height above the horizontal form where the ball is hit, 
angle of projectile above the horizontal, 
initial speed of the projectile, 
<u>Firstly we find the </u><u>vertical component of the initial velocity</u><u>:</u>



During the course of ascend in height of the ball when it reaches the maximum height then its vertical component of the velocity becomes zero.
So final vertical velocity during the course of ascend:
Using eq. of motion:
(-ve sign means that the direction of velocity is opposite to the direction of acceleration)

(from the height where it is thrown)
<u>Now we find the time taken to ascend to this height:</u>



<u>Time taken to descent the total height:</u>
- we've total height,


- during the course of descend its initial vertical velocity is zero because it is at the top height, so



<u>Now the total time taken by the ball to hit the ground:</u>



Answer:
frequency is 195.467 Hz
Explanation:
given data
length L = 4.36 m
mass m = 222 g = 0.222 kg
tension T = 60 N
amplitude A = 6.43 mm = 6.43 ×
m
power P = 54 W
to find out
frequency f
solution
first we find here density of string that is
density ( μ )= m/L ................1
μ = 0.222 / 4.36
density μ is 0.050 kg/m
and speed of travelling wave
speed v = √(T/μ) ...............2
speed v = √(60/0.050)
speed v = 34.64 m/s
and we find wavelength by power that is
power = μ×A²×ω²×v / 2 ....................3
here ω is wavelength put value
54 = ( 0.050 ×(6.43 ×
)²×ω²× 34.64 ) / 2
0.050 ×(6.43 ×
)²×ω²× 34.64 = 108
ω² = 108 / 7.160 ×
ω = 1228.16 rad/s
so frequency will be
frequency = ω / 2π
frequency = 1228.16 / 2π
frequency is 195.467 Hz