Back(II) Pelicans tuck their wings and free-fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.
A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. 2–49). From what height above the top of the window did the stone fall?
(III) A toy rocket moving vertically upward passes by a 2.0-m-high window whose base is 8.0 m above the ground. The rocket takes 0.15 s to travel the 2.0 m height of the window. What was the launch speed of the rocket, and how high will it go? Assume the propellant is burned very quickly at blastoff.
A person jumps out a fourth-story window 18.0 m above a firefighter's safety net. The survivor stretches the net 1.0 m before coming to rest, Fig. 2–50. (a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net? (b) What would you do to make it 'safer' (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain. <IMAGE>
Suppose a car manufacturer tested its cars for front-end collisions by hauling them up on a crane and dropping them from a certain height. What height corresponds to a collision at 35 km/h?
A rocket rises vertically, from rest, with an acceleration of 3.2 m/s² until it runs out of fuel at an altitude of 725 m. After this point, its acceleration is that of gravity, downward. What maximum altitude does the rocket reach?
A helicopter is ascending vertically with a constant speed of 6.40 m/s. At a height of 105 m above the Earth, a package is dropped from the helicopter. How much time does it take for the package to reach the ground? [Hint: What is v₀ for the package?]
Suppose a 65-kg person jumps from a height of 3.0 m down to the ground. What is the speed of the person just before landing (Chapter 2)?
<IMAGE>
Two children are playing on two trampolines. The first child bounces up one-and-a-half times higher than the second child. The initial speed upwards of the second child is 4.0 m/s. What is the initial speed of the first child?
A parachutist bails out of an airplane, and freely falls 75 m (ignore air friction). Then the parachute opens, and her acceleration is ― 1.5 m/s² (up). The parachutist reaches the ground with a speed of 1.5 m/s. From how high did she bail out of the plane?
A rocket in deep space has an empty mass of 150 kg and exhausts the hot gases of burned fuel at 2500m/s . It is loaded with 600 kg of fuel, which it burns in 30 s. What is the rocket's speed 10 s, 20 s, and 30 s after launch?
Bill can throw a ball vertically at a speed 1.5 times faster than Joe can. How many times higher will Bill's ball go than Joe's?
For an object falling freely from rest, show that the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). (This was first shown by Galileo.) See Figs. 2–27 and 2–30.