9. A wide east-west aligned river flows to the east with a uniform velocity of 4.00 [km/h]. A boat with a northward-directed velocity of 8.0 km/h relative to the river is crossing from the south bank of the river to the north bank. The river is 80. [m] wide. (a) What is the velocity of the boat with respect to an observer on the riverbank. (b) How far downstream will the boat make landing on the north bank of the river? (c) How long will it take the boat to cross the river? 10. A projectile is launched from level ground with an initial speed of 40.0 [m/s] at an angle of 60.0 above the horizontal. The projectile lands on a hillside 4.00 [s] later. Neglect air friction. (a) What is the projectile's velocity at the highest point of its trajectory?; (b) How high up on the hill does the projectile land?; (c) How far downrange (i.e., what is the horizontal distance) is the projectile's landing point?; (d) What is the straight-line distance from where the projectile was launched to where it hits the hill? Ch.3 HW 7, 8, 9, 10 7. Rubber tubing is used to launch a water balloon at an angle of 30.0 above the horizontal from the roof of an isolated multi-story building. If the balloon launches from a height that is 40.0 m above the ground and the initial speed of the balloon is 20.0 [m/s], (a) How long does it take before the balloon hits the ground? (b) What is the balloon's speed just before impact? (c) What is the ratio of the balloon's vertical speed just before impact to its horizontal speed? (d) What is the horizontal range of the balloon? (e) What is the maximum height above the ground that the balloon reaches? 8. A ball is projected horizontally from the top of a building. One second later, another ball is projected horizontally from the same point with the same velocity. Answer the following questions about this scenario, making sure to explain your answers: (a) At what point when they are both falling will the balls be closest to each other? (b) Will the first ball always be travelling faster than the second (when they are both in the air)? (c) What will be the time difference between when the balls hit the ground? (d) Can the horizontal speed of the second ball be changed so that the balls arrive at the ground at the same time? If so, how should it be changed?