Question

Help on the second part please (b)

Answer 1

I'll do that with pleasure.  But first, we seriously need to discuss part-A.
The answer to part-A is used to solve part-B, and you don't have it yet.

I loved the way you set up part-A ... started out with the formula you'll use
to solve it, then listed the given information neatly, and substituted the given
information into the formula.  All of that was so beautifully laid out ... with
units and everything, which hardly anybody ever does ... that I didn't notice
the absurd result at first.

Angie !  Take two steps back and look over part-A !  You multiplied
(200 and something) by (100 and something), and got an answer of
(200 and something) !  What's up with that ? ! ?

Everything outside the box is correct and beautiful ... units and everything.
Inside the box should be    30,021 kg-m/s .

NOW we're equipped to work on part-B:

You start out with  F = m a .
That's the best formula to use for roughly 99.9% of these motion problems ...
but not for this one, sadly.

Here's what you need for part-B.  Again, I love the way you start out listing
the formula you're going to use, and all the data you know.
But I think the whole subject of 'Impulse' temporarily slipped your mind.
Here's a quick review:

-- (force) acting for (some limited time) is called "Impulse".
-- The magnitude of impulse is (force) x (time).
-- Impulse is a vector.  The direction of impulse is the direction of the force.
-- Look at the units.  (I wouldn't do this with anyone else, but you're different ...
you have an understanding and appreciation for units.)

force = 'newton' = kg-m/s²
time = second

Impulse = (force)    · (time)

            = (kg-m/s²) · (sec)  =  kg-m/s .      Same units as momentum !

It turns out that the amount of impulse is exactly the amount of
change in momentum !

You push on an object with (some force) for (some time).
Then you stop pushing and you let the object go on its way.
The impulse you delivered to the object is (force) x (time), and that's
exactly how much momentum you gave it !

NOW ... The motorcycle has  30,021 kg-m/s  of momentum.
In order to stop it ...
  that's how much momentum it needs to lose.
OR
  that's how much impulse you have to give it, opposite to its motion.

                           (Force) x (time)  =  30,021 kg-m/s

Divide each side
by  t = 0.05 sec:     Force              =  (30,021 kg-m/s) / (0.05 sec)

                                                    = (30,021 / 0.05)  kg-m/s²

                                                    =      600,423 newtons

                                                    (roughly 135,000 pounds)
           
                                                    (That's why a motorcycle crash                    
                                                     can often mess up your hair.
                                                     Or worse. )