1. In a collision, a car is brought to a stop in 2 s. In a second collision, a similar car moving at the same speed is brought to a stop in 4 s. Compare the forces which act upon these two cars during the collisions. 2. Explain why it is dangerous for a person to jump from a 5-m height to a concrete sidewalk while it is quite safe to jump from the same height into a pile of hay. 3. A braking force is applied to a 300-kg motorcycle to reduce its speed from 20.0 m/s to 16.0 m/s in 10.0 s. Find (a) the initial momentum of the motorcycle; (b) the final momentum; (c) the braking force