A spur gear with $20^{\circ}$ full depth teeth is transmitting $20 \: kW$ at $200 \: rad/s$. The pitch circle diameter of the gear is $100 \: mm$. The magnitude of the force applied on the gear in the radial direction is
1. $0.36 \: kN$
2. $0.36 \: kN$
3. $1.39 \: kN$
4. $2.78 \: kN$