Firstly, sometimes mac would have detected the drive but it might not be listed in the finder's device list. To solve that Go to Finder menu -> Preferences -> Sidebar -> Devices and ensure to check "External Disks" in devices section.
If that doesn't help, here's the solution.
I found that the Hp pendrives comes with Write-Protection enabled by default for added security purposes in virus-prone environments
So if you have not formatted the disk atleast once in mac/windows and inserting a brand new product then this issue comes up.
If you have a windows machine go ahead and format pen drive once there and pop it back into mac to make it up and running.
However, if you dont own a windows machine and wanted to make it work in Mac the following steps will help you
1. Go to Disk Utility
2. Find USB in medias (HP v210w in this case)
3. Go to Erase Tab
4. Pick "MS-Dos Fat" file system and Erase the disk.
Thats all the disk is now detected and mounted in mac as well..