While slowing for traffic, I was struck in the rear by a large pickup. On impact, the driver seat broke, causing the whole seat to tilt back to more than 45 degrees backwards tilt. This caused me to impact the seat at a greater impact than I would have had if the seat remained in place. The seat being in that position after the impact, made it so I could not reach the pedals (brakes) to stop the vehicle from rolling forward until I used the steering wheel to pull myself forward. Upon inspection after the collision, it was observed that part of the adjustment assembly detached from a bolt causing the seat to come loose from its proper position.