Question

A ball is dropped from a roof top of a building and was observed to reach the ground in 2 seconds. Its speed at that time is

Answer 1

Answer :

• The speed of the ball at reaching the ground is 20 m/s

Explanation :

Given :

• Time to reach the ground, t = 2 s
• Acceleration due to gravity, g = 10 m/s²
• Initial velocity of the ball, u = 0 m/s

To find :

• Velocity with which the ball will strike the ground, v = ?

Knowledge required :

Second equation of motion :

⠀⠀⠀⠀⠀⠀⠀⠀⠀h = ut + ½gt²

Where,

• h = height
• u = Initial velocity
• g = Acceleration due to gravity
• t = Time Taken

Third equation of motion :

⠀⠀⠀⠀⠀⠀⠀⠀ v² = u² + 2gh

Where,

• h = height
• u = Initial velocity
• g = Acceleration due to gravity
• v = Final velocity

Solution :

First let us find the height of the tower :

By using the second equation of motion and substituting the values in, we get :

⠀⠀=> h = ut + ½gt²

⠀⠀=> h = 0(2) + ½ × 10 × 2²

⠀⠀=> h = 0 + ½ × 10 × 2²

⠀⠀=> h = ½ × 10 × 4

⠀⠀=> h = 10 × 2

⠀⠀=> h = 20

⠀⠀⠀⠀⠀⠀⠀⠀⠀∴ h = 20 m

Hence the height of the tower is 20 m.

Now,

To find the velocity of the ball :

By using the third equation of motion and substituting the values in it, we get :

⠀⠀ => v² = u² + 2gh

⠀⠀ => v² = 0² + 2 × 10 × 20

⠀⠀ => v² = 0 + 400

⠀⠀ => v² = 400

⠀⠀ => v = √400

⠀⠀ => v = 20

⠀⠀ ⠀⠀ ⠀⠀ ⠀⠀∴ v = 20 m/s

Therefore,

• Velocity with which the ball will strike the ground, v = 20 m/s

Answer 2

Hello mate !

Question:-

• A ball is dropped from a roof top of a building and was observed to reach the ground in 2 seconds. Its speed at that time is

Given :-

• Time in reaching the ground = 2 seconds.
• Acceleration due to Gravity = 10 m/s² (we can take g as 10m/s² if it's not given in the Ques.)
• initial velocity = 0 m/s

To find :-

• Final velocity.

Formulas to be used :-

• second equation of motion :-

h = ut + ½gt²

• third equation of motion :-

v²= u²+2gh

Solution :-

let's find the value of h first by using Second law of motion:-

⇒ h = ut +½gt²

⇒ h = 0(2)+½(10)(2)²

⇒ h = 0 + 5(4)

⇒ h = 20 m

hence the value of h is 20m

now we need to find the value of v by using third law of motion:-

⇒ v²= u²+2gh

⇒ v²= (0)²+2(10)(20)

⇒ v²= 0 + 400

⇒ v² = 400

⇒ v =√400

⇒ v = 20 m/s.

so finally, we got the value of v i.e final velocity as 20m/s.

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Hope it helps ⭐⭐⭐