#### Answer

The magnitude of the force exerted by the locomotive on the caboose is $3.5~N$

#### Work Step by Step

The caboose accelerates at $3.0~m/s^2$. We can find the net force on the caboose:
$\sum F = ma = (1.0~kg)(3.0~m/s^2) = 3.0~N$
We can find the force $F_l$ exerted on the caboose by the locomotive:
$F_l-F_f = \sum F$
$F_l = \sum F+F_f$
$F_l = 3.0~N+0.50~N$
$F_l = 3.5~N$
The magnitude of the force exerted by the locomotive on the caboose is $3.5~N$