A 20kg tennis ball has a initial velocity of 10m/s is rolling on a rough surface slope which have a kinetic friction of 200N and continuously accelerate 70m/s. How long will it take for the tennis ball to stop?
Tennis ball of 20kg? I don't think so!
If it is continuously accelerating at 70 m/s^2, it will never stop.
You need to state your question more clearly, noting how the friction acts against the motion. F=ma