1) At the moment of being at the top, the piston will not only tend to push the penny up but will also descend at a faster rate at which the penny can reach in 'free fall', in that short distance. Therefore, at the highest point, the penny will lose contact with the piston. Therefore the correct answer is C.
2) To solve this problem we will apply the equations related to the simple harmonic movement, hence we have that the acceleration can be defined as

Where,
a = Acceleration
A = Amplitude
= Angular velocity
From a reference system in which the downward acceleration is negative due to the force of gravity we will have to



From the definition of frequency and angular velocity we have to




Therefore the maximum frequency for which the penny just barely remains in place for the full cycle is 2.5Hz
In the diagram, the ship send sound(?) waves to the water, to determine if there is anything there. If there is something like a sunken ship shown in the diagram, the waves return in a shorter time hence you can understand if theres something or now. This is the principle of radars and sonars.
Explanation :
A circuit is the representation of the path of the flow of current. The circuit can be either closed or open.
When the switch is off the circuit is closed circuit and when the switch is not connected the circuit is open.
The items that are sufficient to make a circuit are as follows :
- Voltage source like a battery.
- Resistors or electrical equipment like heater, motor etc.
Other components can be ammeter, voltmeter, ac source, variable resistors etc.
Yep that's correct
And transverse waves move perpendicular to the direction of energy transport