You and a friend are sitting on a cliff, tossing pebbles over the edge, either s

Question

You and a friend are sitting on a cliff, tossing pebbles over the edge, either straight up or straight down, so that they land in the lake below. Your pebble is in free fall for 5 seconds, with a final speed of 30m/s. Which way is the pebble going when it hits the lake? How fast and in what direction did you throw the pebble? When was the pebble at its maximum height, assuming it left your hand at t = 0? What was the pebble's maximum height? How high is the cliff? How much work did the Earth (meaning, the Earth's gravitational force) do on the pebble? Assume the pebble's mass is 0.05kg

Explanation / Answer

a)

in downward direction

b)

Vo = initial velocity

Vf = final velocity = 30 m/s

a = acceleration = 9.8 m/s2

t = time = 5 sec

using the equation

Vf = Vo + at

30 = Vo + 9.8 x 5

Vo = -19 m/s

negative sign indicate upward direction

c)

at maximum height ,

Vf = 0

using the equation

Vf = Vo + at

0 = - 19 + 9.8 t'

t' = 1.94 sec

d)

h = maximum height above the cliff

using the equation

h = Vo t' + (0.5) a t2

h = (-19) (1.94) + (0.5) (9.8) (1.94)2

h = - 18.42 m

negative sign indicate upward direction

e)

H = height of cliff

using the equation

H = Vo t' + (0.5) a t2

H = (-19) (5) + (0.5) (9.8) (5)2

H = 27.5 m

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.