Asled and rider, gliding over horizontal, frictionless ice at 4.7 m/s , have a combined mass of 80 kg . the sled then slides over a rough spot in the ice, slowing down to 3.4 m/s . what impulse was delivered to the sled by the friction force from the rough spot? express your answer to two significant figures and include the appropriate units.

Impulse is the change in momentum.
All we need is the momentum before and after.

Momentum  =  (mass) x (speed)

Before:        =  (80 kg) x (4.7 m/s)  =  376 kg-m/s

After:           =  (80 kg) x (3.4 m/s)  =  272 kg-m/s

Change in momentum  =  (376 - 272) =  104 kg-m/s

Notice that when you work with impulse, you're USUALLY calculating

                           (force) x (time).

The force is in Newtons, and the time is in seconds,
so the impulse is usually in units of

                             Newton-seconds .

So how can I say that impulse and change of momentum are
the same thing ?  Am I trying to pull a fast one on you ?

Remember that    1 Newton is  1 kg-m/s²

So                       (force) x (time) 

                     =  (Newton) x (second) 

                     =  (kg-m/s²) x (second)  =  kg-m/s .

and  Momentum = (mass) x (speed)  =  (kg) x (m/s)

The units of impulse are the same as the units of momentum !

So when you give an object some impulse, you give it exactly
that much momentum.