Answer:
d. The ideal diode acts as a short circuit for forward currents and as an open circuit with reverse voltage applied.
Explanation:
Ideal diode acts like an ideal conductor. In case of forward voltage it acts like an ideal conductor. However when it is reverse biased then it behaves like an ideal insulator. You can understand it bu considering a switch. When the voltage is forward then ideal diode acts like a closed switch. When the voltage is reverse biased then ideal diode behaves like an open switch.
That is why we can say that the ideal diode acts as a short circuit (higher conduction) for forward currents and as an open circuit ( zero conduction) with reverse voltage applied.
Answer:
Part a)

Part b)

Explanation:
Part a)
as the mass of the suspension system is given as

also we have

so now for force balance we have



Part b)
Now we know that amplitude decreases by 63% in each cycle
so after one cycle the amplitude will become 37% of initial amplitude
so it is given as

also we know




here t = time period of one oscillation
so it is



now damping constant is


here we know that the speed of the signal is same as the speed of light
so here we will have

the altitude of the airplane is given as

now we know that time taken by the signal to reach the control tower is given as

now it is given as


so above is the time taken by the signal to reach the control tower