Momentum = (mass) x (speed)
You haven't mentioned the speed of the 3-ton mouse.
Let's say that Jabba the Mouse is running as fast as he can ...
1 centimeter per day = 1 meter / 8,640,000 seconds.
Then his momentum is (3,000 kg-m/8,640,000 sec) = 3.472 x 10⁻⁴ kg-m/sec
For Jerry the normal-size mouse to have the same momentum,
(0.25 kg) x (speed) = 3.472 x 10⁻⁴ kg-m/sec
Divide each side by (0.25 kg): Speed = 3.472 x 10⁻⁴ / 0.25 m/s
= 1.388 x 10⁻³ m/s
= 1.388 millimeter per second.
A normal mouse can definitely attain this speed yes.
Even faster if he is startled or scared, or pursuing a girl mouse.
