Question

a boy can jump 5m vertically what must be the inital velicity of the boy assume g=9.8m/s​

Answer 1

Given :

➳ Max. vertical height = 5m

➳ Acc. due to gravity = 9.8m/s²

To Find :

➠ Initial velocity of boy.

Concept :

➝ Final velocity of boy will be zero because acceleration due to gravity continuously acts in downward direction.

➝ For a body thrown vertically upward, g us taken as negative.

✭ Third equation of kinematics :

• v² - u² = 2as

Calculation :

⇒ v² - u² = 2(-g)H

⇒ (0)² - u² = -2(9.8)(5)

⇒ u² = 98

⇒ u = √98

⇒ u ≈ 10m/s

Answer 2

$\bigstar$ $\sf{\pink{\underline{\underline{\blue{To\:Find:-}}}}}$

• The initial Velocity(u) of Boy .

$\bigstar$ $\sf{\blue{\underline{\underline{\purple{SOLUTION:-}}}}}$

☞ GIVEN :-

• A boy can jump 5m vertically .

1. Height = 5 m
2. g (gravitational acceleration) = 9.8 m/s²

☞ FORMULA :-

• when Acceleration of body is constant , then the Equation of Motion is,

$\checkmark\:\tt{\orange{\underline{\boxed{v^2\:-\:u^2\:=\:2as\:}}}}$

☞ CALCULATION :-

♻️ When boy can jump vertically upward, then the velocity is upward direction but the acceleration(due to gravity) of the boy is downward direction and gravitational Acceleration is acting on the boy . So, Acceleration is negative as sign .

♻️ The final velocity of boy is “zero” when he reaches the height of “5m” and the acceleration is “9.8m/s²”.

• v (final velocity) = 0 m/s

• g (acceleration) = -9.8 m/s²

• s (distance or height) = 5 m

☞ Now, put the formula and get the Answer .

$\tt{\red{v^2\:-\:u^2\:=\:2as\:}}$

$\tt{\implies\:0^2\:-\:u^2\:=\:2\times{(-9.8)}\times{5}\:}$

$\tt{\implies\:u^2\:=\:98\:}$

$\tt{\implies\:u\:=\:{\sqrt{98}}\:}$

$\tt{\implies\:u\:=\:9.89\:m/s\:}$

$\bigstar\:\underline{\boxed{\bf{\red{Required\:Answer\::\:initial\:velocity(u)\:=\:9.89\:m/s\:}}}}$