Answer:
-2200 N
Explanation:
Here we can use the impulse theorem, which states that the impulse exerted on Sarah (product of force and duration of collision) is equal to Sarah's change in momentum:

where
F is the average force
is the duration of the collision
m is the mass
is the change in velocity
In this problem:
m = 55 kg

Solving the formula, we find the force exerted by the seatbelt on Sarah:

And the negative sign means the direction is opposite to that of Sarah's initial motion.
Answer:
Speed BA = 18 km/hr.
Explanation:
Given the following data;
Speed AB = 30km/hr
Speed BA = x km/hr
Average speed = 24 km/hr
To find the value of x;
Average speed = (Speed AB + Speed BA)/2
Substituting into the equation, we have
24 = (30 + x)/2
48 = 30 + x
x = 48 - 30
x = 18 km/hr