The forces that a and b exert on each other are very large but last for a very short time. if we choose a time interval from just before to just after the collision, what is the approximate value of the impulse applied to the two-object system due to forces exerted on the system by objects outside the system?

Zero

Explanation:

Newtons second law says that the instantaneous force exerted on a body during an interval of time t, is exactly de definition of Impulse

When there is a collision, there is a change on the linear momentum of each object due to the force the other exerts on in. And we can measure the impulse applied to one of the objects due to the force the other exerts on it.

But if we consider our system made of the two bodies,  there are no external forces on it. And so the impulse due to external forces is 0!

Hope my answer helps.

Have a nice day!

5 w for 1hr = 5x60x60 joules=300x60=3000x6=18,000j as total energy conversion. efficiency of bulb needed for radiant to thermal within 18000

this is poiselle's equation from fluid mechanic in physics. mech eng