If we are to ride on a hyperloop train, can ordinary man withstand the G force?
Yes, an ordinary man (or woman) would easily withstand the G-force when accelerating or decelerating. Keep in mind that a hyperloop pod wouldn't go appreciably faster than a commercial airplane; maybe 100 mph faster. Also, there has already been supersonic commercial airplanes in the past such as the Concorde and the Tupolev Tu-144 so the speed that a hyperloop pod would travel wouldn't be a first for commercial travel.

G-force is only felt during acceleration and deceleration. While a hyperloop pod is moving straight at a constant speed the sensation for the passengers of a hyperloop pod would be similar to cruising in a plane.
The beauty of the hyperloop transport (it's not a train) is that the G force can be controlled unlike other fast moving transportation like Aircraft, Hypersonic Aircraft, Rockets, even regular SuperTrains that have efficiency reasons needed for minimal rapid acceleration.

So the answer is not just yes, it can be the most comfortable G-force wise, super fast way to travel.
okay maybe one more question then today .... musing addiction

the problem with hyperloop wouldnt be the g-force on accelleration but the off-chance of a natural disaster.

say you get an earthquake of a certain magnitude and a section of the tunnel collapses, the train would either have to be able to stop SO fast that your grannys false teeth go flying or

if it cant it would probably be like being stuck in a giant steel accordeon going from (as i read on wiki) 1200km/h to zero in a fraction of a second, closing

it would be human mousse

thats my shortest answer ever, i deserve an achievement for this @arcange ? :p
Acording to a research( my source is wikipedia) a human can survive 20g for 10 seconds, 10g for more than 6 minutes and 4g and lower for more than 10 minuites before they blackout or blood vessels in their head starts to pop. But the case is different when you are facing a horizontal acceleration. When you go upwards or downwards your acceleration works with or against earths g. But when you accelerate forward or backword you are just creating linear drag over g. Because of the g drag being perpendicular to your spine you will feel less severe effects than vertical acceleration.

Now to accurately claculate, once the hyperloop takes on cruising speed of say 500 mph you will feel nothing.. as you are not being dragged against your initial inertia. But hyperloop can accelerate from zero to 60 in one second which is equal to 6.7 g.. It will be tough to handle that amount of g only in that time of acceleration . But hyperloop will never accelerate with that speed if humans are onboard.. they will have a safety limit of say at most 2g at maximum. Every human including childs are able to handle 33.8 meters of acceleration per second which is more than 3 gs And I'm sure they will not increase it to that amount at once.. instead the initial acceleration will be broken into some phases.