Collision domain is a portion in the network where there is a possibility of formation of packets. This occurs when two or more devices are able to send a packet to a single switch or port on the network that is shared, on the same time. It was noted that this collision domain reduces the efficiency of the network.
For this item, the first packet is the whole switch with the three devices. Next one would be first of the three devices that is connected to the other port. Similarly, the third one would be the second of the three devices that is also connected to the switch. Therefore, the answer is 3.
A) 
The energy of an x-ray photon used for single dental x-rays is

The energy of a photon is related to its wavelength by the equation

where
is the Planck constant
is the speed of light
is the wavelength
Re-arranging the equation for the wavelength, we find

B) 
The energy of an x-ray photon used in microtomography is 2.5 times greater than the energy of the photon used in part A), so its energy is

And so, by using the same formula we used in part A), we can calculate the corresponding wavelength:

Answer:
impulse = force x time
impulse = 1900000 x 0.005 = 9500Ns