Question

14. A ball is thrown vertically upwards. It
reaches its maximum height in 2.5 s. If the
acceleration of the ball 10 m/s2 be directed
towards the ground, find the initial velocity
of the ball
(Ans. 25 m/s)
​

Answer 1

t=2.5s

g=-10m/s^2

v=0

u=?

from first equation of motion

v=u+at

0=u+(-10)*2.5

25=u

hence intial velocity is 25 m/s

NOTE : when ball is thrown vertically upwards it means it is being thrown on the opposite of the motion so thats why we use (-) sign in acceleration

• when ball will be at its maximum height its (v) will always be 0

Answer 2

Answer:

initial velocity of the ball

➪ 25 m/s

Step by step explanations :

given that,

A ball is thrown vertically upwards. It

reaches its maximum height in 2.5 s.

let the maximum height reached by ball be h

here,

final velocity of the ball = 0 m/s

[ball will at rest at its maximum height]

time taken to reach maximum height = 2.5 seconds

let the initial velocity by which ball was thrown be u

now we have,

initial velocity(u) = u

final velocity(v) = 0 m/s

gravitational acceleration(g) = -10 m/s²

time taken(t) = 2.5 s

by the gravitational equation of motion,

v = u + gt

putting the values,

0 = u + (-10)(2.5)

u - 25 = 0

u = 25 m/s

so,

initial velocity of the ball

➪ 25 m/s