Answer:
5.5 × 10^14 Hz or s^-1
no orange light has less frequency so no photoelectric effect
Explanation:
hf = hf0 + K.E
HERE h is Planck 's constant having value 6.63 × 10 ^-34 J s
f is frequency of incident photon and f0 is threshold frequency
hf0 = hf- k.E
6.63 × 10 ^-34 × f0 = 6.63 × 10 ^-34× 6.66 × 10^14 - 7.74× 10^-20
6.63 × 10 ^-34 × f0 = 3.64158×10^-19
f0 = 3.64158×10^-19/ 6.63 × 10 ^-34
f0 = 5.4925 × 10^14
f0 =5.5 × 10^14 Hz or s^-1
frequency of orange light is 4.82 × 10^14 Hz which is less than threshold frequency hence photo electric effect will not be observed for orange light
The change in electric potential energy of the ion is equal to the charge multiplied by the voltage difference:

where the charge q of the na+ ion is equal to one positive charge, so it's equal to the proton charge:

, and Vf and Vi are the final and initial voltages.
Substituting the numbers, we find:
1) Focal length
We can find the focal length of the mirror by using the mirror equation:

(1)
where
f is the focal length

is the distance of the object from the mirror

is the distance of the image from the mirror
In this case,

, while

(the distance of the image should be taken as negative, because the image is to the right (behind) of the mirror, so it is virtual). If we use these data inside (1), we find the focal length of the mirror:

from which we find

2) The mirror is convex: in fact, for the sign convention, a concave mirror has positive focal length while a convex mirror has negative focal length. In this case, the focal length is negative, so the mirror is convex.
3) The image is virtual, because it is behind the mirror and in fact we have taken its distance from the mirror as negative.
4) The radius of curvature of a mirror is twice its focal length, so for the mirror in our problem the radius of curvature is:
Conservation of linear momentum:
m*v inital = m*v final
0.06*0.7 + 0.03*0 = 0.06*(-0.2) + 0.03*v
(my algebra, or use ur calculator: 0.06*.07=0.042, etc ... or ur teacher may think you got some help)
0.06*(0.7+0.2)=0.03*v, v = 0.06*0.9/0.03=1.8 m/s
Answer 1.8 m/s (positive, to the right).