Question

An object thrown vertically upwards reaches height of 500m. What was its initial velocity? How long will it

take to come back to the earth? Assume g = 10m/s​

Answer 1

Explanation:

Let the initial velocity = u

final velocity = v

v= 0 m/s

s = 500 m 

2as = v²-u²

2 (-10) 500 = u²

u = 100 m/s

Hence initial speed is 100 m/s

Now,

v = u + at

0 = 100 - 10 t

t = 10 s

total time taken = 20 sec(while going upward and coming

downward).

Answer 2

GIVEN :

• Height, h = 500 m.
• Assume, gravity, g = 10 m/s.
• V = 0 m/s.

FORMULA USED :

• V = u + at.
• 2gs = v² - u².

Here,

u = Initial velocity.

v = Final velocity.

a = acceleration.

t = time taken.

g = gravity.

s = distance.

TO FIND :

• Initial velocity, u = ?
• How long will the object take to come back to the earth.

SOLUTION :

Now using the formula,

2gs = v² - u².

Put the given values in the above formula,

$\implies$ 2(-10) 500 = u²

$\implies$ 2(-10) × 500 = u²

$\implies$ u = 100 m/s.

•°• Initial velocity will be 100 m/s.

Now to find time, t = ?

we know that,

v = u + at

Put the values in the above formula,

$\implies$ 0 = 100 - 10t

$\implies$ t = 100/10

$\implies$ t = 10 sec.

•°• The total time taken is 20 sec.