18.4 On a planet that has no atmosphere, a rocket 14.2 m tall is resting on its launch pad. Freefall acceleration on the planet is
4.45 m/s^2. A ball is dropped from the top of the rocket with zero initial velocity. (a) How long does it take to reach the launch
pad? (b) What is the speed of the ball just before it reaches the ground?
(a) s
(b) m/s18.5 To determine freefall acceleration on a moon with no atmosphere, you drop your handkerchief off the roof of a baseball
stadium there. The roof is 113 meters tall. The handkerchief reaches the ground in 18.2 seconds. What is freefall acceleration
on this moon? (State the result as a positive quantity.)
m/s^218.6 You are a bungee jumping fanatic and want to be the first bungee jumper on Jupiter. The length of your bungee cord is
45.0 m. Freefall acceleration on Jupiter is 23.1 m/s^2. What is the ratio of your speed on Jupiter to your speed on Earth when
you have dropped 45.0 m? Ignore the effects of air resistance and assume that you start at rest.
18.7 On the Apollo 15 space mission, Commander David R. Scott verified Galileo's assertion that objects of different masses
accelerate at the same rate. He did so on the Moon, where the acceleration due to gravity is 1.62 m/s^2 and there is no air
resistance, by dropping a hammer and a feather at the same time. Assume they were 1.25 meters above the surface of the
Moon when he released them. How long did they take to land?
s18.8 You stand near the edge of Half Dome in Yosemite, reach your arm over the railing, and (thoughtlessly, since what goes up
does come down and there are people below) throw a rock upward at 8.00 m/s. Half Dome is 1460 meters high. How long
does it take for the rock to reach the ground? Ignore air resistance.s18.9 To get a check to bounce 0.010 cm in a vacuum, it must reach the ground moving at a speed of 6.7 m/s. At what velocity
toward the ground must you throw it from a height of 1.4 meters in order for it to it have a speed of 6.7 m/s when it reaches
the ground? Treat downward as the negative direction, and watch the sign of your answer.
m/s18.10Two rocks are thrown off the edge of a cliff that is 15.0 m above the ground. The first rock is thrown upward, at a velocity of
+12.0 m/s. The second is thrown downward, at a velocity of í12.0 m/s. Ignore air resistance. Determine (a) how long it takes
the first rock to hit the ground and (b) at what velocity it hits. Determine (c) how long it takes the second rock to hit the ground
and (b) at what velocity it hits.
(a) s
(b) m/s
(c) s
(d) m/s
18.11A person throws a ball straight up. He releases the ball at a height of 1.75 m above the ground and with a velocity of
12.0 m/s. Ignore the effects of air resistance. (a) How long until the ball reaches its highest point? (b) How high above the
ground does the ball go?
(a) s
(b) m18.12To determine how high a cliff is, a llama farmer drops a rock, and then 0.800 s later, throws another rock straight down at a
velocity of í10.0 m/s. Both rocks land at the same time. How high is the cliff?
m