In Game Of Thrones, John Snow swats a guy off his horse with a sword strike (a similar thing can be seen in The Norseman trailer). How much energy is required to do this? What kind of force?
The horse's speed
From behind-the-scenes footage, I'd guess the horse is going about 8 m/s. The guy riding it, therefore, if he has a mass of 80 kg, has a momentum of 640 kg*m/s.
The force of the hit
For John to knock the guy off the horse, he has to negate the enemy's forward momentum. In fact, the guy gets knocked back about 2 m at roughly 3 m/s, so he has to do more than that. Force applied is momentum divided by time of impact, so:
(640 + 240) ÷ ~0.01 = ~88,000 Newtons (rougher calculations indicate that the pressure was about 50 MPa, disregarding any... squishiness of the target)
The energy transfer of the hit
The pre-hit energy of the dude on the horse is about 2.5kJ. His after-hit energy was about 300J, but he was traveling in the opposite direction. John had to impart about 2800J of kinetic energy (in VSBW terminology [ew!], this is Street level).
This is a bit high (professional baseball players can swing a bat fast enough to store approximately 1kJ) but, you know, not completely ridiculous.
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