If the load is 4kg and the distance between the shaft and load is 5cm. We can use torque to measure it. As we know the torque of the motor is 1176mN.m, and that equals to 1.176Nm (SI unit).
Torque= Force x Lever arm
= 40N x 0.05m
= 2 Nm
**4Kg = 40N (W=mg)
Therefore the motor is not capable to accomplish the job. But you can try this motor SPG50-180K
http://www.cytron.com.my/viewProduct.php?pcode=SPG50-180K&name=DC%20Geared%20Motor It has 1.96Nm of torque, should be close enough for your project. But it could take in lots of current.
Hope this helps!