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Answer:
2.9 E14 Hz
Explanation:
As we know by Einstein's equation that energy incident on the photo sensitive surface will be used by the surface to eject electron out of the surface with some kinetic energy.
This is given by

now the threshold frequency is the minimum frequency of the incident photons due to which electrons are ejected out with minimum kinetic energy or least kinetic energy.
So here when KE = 0 in the graph then corresponding to that position the frequency will be given as threshold frequency
so here from graph when KE = 0

Answer:
option C
Explanation:
The correct answer is option C.
The normal force is the force exerted by the biker on the inner vertical surface of the circular track.
When the biker move in the circular track centripetal force is acting on the biker which is being balanced by the normal force.
To overcome the gravitation force on the biker the velocity of the biker should be high such that centripetal acceleration of the biker can overcome the gravity force acting on the biker.
Length•Width•Height is the answer