Originally Posted by
mikeshoup
F = ma. They would both carry the same force if they're at a constant velocity. (That's zero newtons)
Kinetic Energy otoh, is a 100kg cyclist travelling 50mph carries a substantial more amount of kinetic energy than a 1500kg car travelling 5mph.
KE = 0.5mv^2
KE bike = 0.5*100kg*(50mi/hr)^2 = 125000 kg*(mi/hr)^2 (which is the strangest unit for energy ever, but valid none the less)
KE car = 0.5*1500kg*(5mi/hr)^2 = 18750 kg*(mi/hr)^2
KE bike / KE car = 6.67.
The bike carries 6.67 times more kinetic energy than the car.
Its okay, high school physics was a long time ago for me as well.
While the bike would have most of the energy, the force of the collision will be the same on both the cyclist and the car (Newton's third law), and you could get a (really) rough estimate by doing the change in the rider's momentum over the very small time period. The difference is that the driver is protected by a ****-ton of metal, and the rider is, at most, protected by an inch of styrofoam on his or her head.