Answer
The magnitude of $F_B$ is $~~3700~N$
Work Step by Step
We can find the required centripetal force to keep the car moving in a circle:
$F = \frac{mv^2}{r}$
$F = \frac{(5000~N/9.8~m/s^2)(5.0~m/s)^2}{10~m}$
$F = 1300~N$
Note that at the top of the circle, the centripetal force is directed straight down.
Let downward forces be positive.
We can find the force $F_B$:
$mg+F_B = 1300~N$
$F_B = 1300~N-mg$
$F_B = 1300~N-5000~N$
$F_B = -3700~N$
The magnitude of $F_B$ is $~~3700~N$
