i need it asap

1- physical topologies
Why is there a need to differentiate between logical and physical topologies?
Is there a case where a network is using one logical topology and a different physical topology?  If yes, give example.  If no, why not?
 
2- Network topology
You have been hired to design and implement a network. The client has a small number of users in a single office location. The client wants to use a topology that runs at 100 megabits per second (Mbps) and allows new systems to be added easily to the network. The client is concerned with cost and maintenance issues, such as cable failures that would cause the network to go down. Given this scenario, what topology would you recommend to the client and how your solution will address client’s issues?  Explain your answer.
 
3- VLAN
VLANs do not save you the cost or administrative requirements of having routers. Nonetheless, Network administrators like to implement VLANs and consider them to be a worthwhile architecture. Discuss why this might be so, or if you disagree, discuss your reasons.