A child stands on the edge of the cliff $10 m$ above the ground and throws a stone horizontally with an initial speed of $5 \,ms ^{-1}$ Neglecting the air resistance, the speed with which the stone hits the ground will be ______$ms ^{-1}$ (given, $g=10 \,ms ^{-2}$ )
- 15
- 20
- 30
- 25
The Correct Option is A
Approach Solution - 1
The correct answer is (A) : 15
\(v_y=\sqrt{2gh}=\sqrt{200}\)
\(v_{net}=\sqrt{25+200}=\sqrt{225}\)
= 15 m/s
Approach Solution -2
Using kinematic equation for vertical motion: \[ v_y = \sqrt{2gh} = \sqrt{200} \] Horizontal velocity remains unchanged: \[ v_x = 5 \text{ m/s} \] Net velocity: \[ v_{\text{net}} = \sqrt{v_x^2 + v_y^2} = \sqrt{25 + 200} = 15 \text{ m/s} \]
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Concepts Used:
Motion in a straight line
The motion in a straight line is an object changes its position with respect to its surroundings with time, then it is called in motion. It is a change in the position of an object over time. It is nothing but linear motion.
Types of Linear Motion:
Linear motion is also known as the Rectilinear Motion which are of two types:
- Uniform linear motion with constant velocity or zero acceleration: If a body travels in a straight line by covering an equal amount of distance in an equal interval of time then it is said to have uniform motion.
- Non-Uniform linear motion with variable velocity or non-zero acceleration: Not like the uniform acceleration, the body is said to have a non-uniform motion when the velocity of a body changes by unequal amounts in equal intervals of time. The rate of change of its velocity changes at different points of time during its movement.