Answer:
40 kilo grammes ...............
1. Frequency: 
The frequency of a light wave is given by:

where
is the speed of light
is the wavelength of the wave
In this problem, we have light with wavelength

Substituting into the equation, we find the frequency:

2. Period: 
The period of a wave is equal to the reciprocal of the frequency:

The frequency of this light wave is
(found in the previous exercise), so the period is:

Answer:
B) Its velocity is perpendicular to the acceleration.
Explanation:
For general projectile motion, the horizontal acceleration is 0 and the vertical acceleration is -g. This is true for all points on the trajectory.
At the highest point, the vertical velocity is 0. So you have only a horizontal velocity as well as a vertical acceleration. So the two are perpendicular.
Answer: The force is directed upward
Explanation: Considering the Lorentz force, given by:
F= qv×B
using the right hand rule and considering the direction of electron velocity and the magnetic field from the figure, the vectorial product gives a force vector upwards .
Answer:
minimum number of photon is 4.05 ×
Explanation:
given data
energy = 50 keV = 50 ×
eV = 50 ×
× 1.602×
J
thickness = 10^-3
contrast = 1%
to find out
number of incident photons
solution
we know here equation that is
E = n × h × ν .......................1
put here all these value
50 ×
= n × 6.6×
× c/ 1× 
50 ×
× 1.602×
= n × 6.6×
×( 3 ×
/ 1×
)
solve it and find n
n = 4.05 ×
so here minimum number of photon is 4.05 ×