Question

A student throws a rock horizontally from the edge of a cliff that is 20 m high. The rock has an initial speed of 10 m/s. If air resistance is negligible, the distance from the edge of the base of the cliff to where the rock hits the level ground below the cliff is most nearly
a. 20 m

b. 5 m

c. 10 m

d. 40 m

Answer 1

Answer:

option A

Explanation:

given,

height of the cliff = 20 m

initial speed = 10 m/s

distance from the edge of the base of the cliff  = ?

now,

time taken to cover vertical distance

initial vertical speed = 0 m/s

using equation of motion

$s = u t + \dfrac{1}{2}gt^2$

$s =\dfrac{1}{2}gt^2$

$t = \sqrt{\dfrac{2s}{g}}$

$t = \sqrt{\dfrac{2\times 20}{9.8}}$

  t = 2 s

in same time the ball will travel horizontal distance

horizontal velocity of ball = 10 m/s

distance = s x t

d = 10 x 2

d = 20 m

Hence, the correct answer is option A