16. What is the instantaneous velocity of a freely falling object 10 s after it is released from rest? What is its average velocity during this 10-s interval? How far will it fall during this time? 17. If you were to walk with a speed of 2.0 m/s for 2.0 h, how far would you travel? 18. The ocean's level is rising about 1.5 mm per year. At this rate, in how many years will sea level be 3 m higher than it is now? 19. The speed of sound in air is about 344 m/s. If you're seated 250 m from home plate at a ball park, how much time passes between seeing a baseball being struck and hearing it? (Hint: Light travels nearly a million times faster than sound.) 20. Johnny Hotfoot slams on the brakes of his car moving at 60 mph (26.7 m/s) and skids to a stop in 4 s. (a) What is the deceleration of the car? (b) How far does it skid? 21. Kenny Klutz drops his physics book off his aunt's high-rise balcony. It hits the ground below 1.5 s later. (a) With what speed does it hit? (b) How high is the balcony? Ignore air drag. 22. You drop your pencil from your desk, which is 1.0 m above the floor. (a) How long does it take for the pencil to hit the floor? (b) How fast is it going just before it hits the floor? 23. Tara Trucker is driving at 27 m/s through a fog that limits her visibility to 30 m. She suddenly sees a car in front of her traveling in the same direction at 10 m/s. If she fails to apply the brakes, how much time does Tara have between seeing the car and crashing into it? * 24. You drive to the city at an average speed of 40 km/h and return at an aver- age speed of 60 km/h. Find your average speed for the entire trip? Explain why the answer is not 50 km/h. * 25. Harry Hopeless averages 40 km/h for the first half of his car trip. How fast should he drive on the remaining half of the trip to have an average speed of 80 km/h for his trip? * 26. A train moves at a constant speed of 60 km/h toward a station 30 km away. At that moment Fanny Fastbird leaves her perch on the locomotive and flies toward the station at a constant speed of 100 km/h relative to the ground. When the bird reaches the station, she immediately turns around and flies back to the train at the same speed. When reaching the train she again imme- diately turns around and flies back to the station, repeating the process until the train passes the station. What total distance is traveled by the bird? 27. Use the time-independent equation for uniformly accelerated motion, final - U. = 2ad, to solve the following: A rocket traveling at 40 m/s accelerates at 2 m/s2. Find its speed when it has traveled 200 m. Uft vo (The equation is derived from d = Vaverage t, where Uaverage solving for t, and then substituting t in the equation d = v.t + zat2). 28. A new test vehicle will accelerate at a steady 4 m/s2 over a 500-m track. How long will the vehicle take to travel the track? * 29. When Valerie Volleyballer jumps to spike a ball, she rises a total of 2.0 m in the air after accelerating through 0.5 m (from crouch to full extension). What is her acceleration during takeoff? *These problems are particularly challenging