Newtons 3rd law states all forces come in pairs which act equally and in opposite directions. The magnet exerts a forward force on the truck and the truck exerts an equal force backwards on the magnet. Because the magnet is physically attached to the truck, there is no way for this to produce a non-zero net force on the system we are trying to move; so the truck will not accelerate.
This is similar to sitting on an office chair with your feet up and trying to push yourself forward by pushing on the back of the chair with your hands. Doesn’t matter how hard you push, the chair will not want to accelerate.
Newtons 3rd law states all forces come in pairs which act equally and in opposite directions. The magnet exerts a forward force on the truck and the truck exerts an equal force backwards on the magnet. Because the magnet is physically attached to the truck, there is no way for this to produce a non-zero net force on the system we are trying to move; so the truck will not accelerate.
This is similar to sitting on an office chair with your feet up and trying to push yourself forward by pushing on the back of the chair with your hands. Doesn’t matter how hard you push, the chair will not want to accelerate.