Which combination of quarks can NOT exist?​

So you can have quark anti-quark pairs (charge anti-charge), or add the charges together (red+blue+green = white). This also holds for theorectical particles made of 4 quarks (2 quarks 2 anti-quarks) and 5 quarks (four quarks and 1 anti-quark or the reverse). In your example ud only has two quarks so only two colour charges so cannot exist. If you want a more indepth answer start reading about colour charge.

Explanation:

0.2 km/m east

Explanation:

The magnitude of Walt's velocity is given by:

where

s is Walt's displacement

t is the time taken

In this problem, Walt's displacement is s=5 km, while the time taken is t=25 m, so the velocity is

and the direction is east, since Walt is running eastwards.