Network Speed : The amount of data which can be transferred through the network in a unit time (Usually measurred in MBPS)
In this page we will understand the minimum packet size that must be sent in order to be able to detect a collision.
This network has a particular speed (which you need to find)
The time required for sending the frame through the channel is found by dividing the packet size by the speed of the network
Now the user node keeps sending the signal for 2 times the travel time for any packet and while any node is sending the data it listens to the channel as well.
So detection of collision also depends on the size of the packet !.
More Explanation @ https://www.youtube.com/watch?v=Zftv3U5_fwI&t=244s