Answer:
-2200 N
Explanation:
The change in momentum of Sarah is equal to the impulse, which is the product between the force exerted by the seatbelt on Sarah and the time during which the force is applied:
[tex]\Delta p=I\\m \Delta v = F \Delta t[/tex]
where
m is the mass
[tex]\Delta v[/tex] is the change in velocity
F is the average force
[tex]\Delta t[/tex] is the duration of the collision
In this problem:, we have:
m = 55 kg is Sarah's mass
[tex]\Delta v = 0-20 = -20 m/s[/tex] is the change in velocity
[tex]\Delta t = 0.5 s[/tex] is the duration of the collision
Solving for F, we find the force exerted by the seatbelt on Sarah:
[tex]F=\frac{m\Delta v}{\Delta t}=\frac{(55)(-20)}{0.5}=-2200 N[/tex]
Where the negative sign indicates that the direction of the force is opposite to that of Sarah's initial velocity.