Question

From the roof top of a 250m tall building an object of mass 01 kg is dropped. Calculate the time which the object will take to reach the earth surface and the velocity with which it will strike the earth’s surface.
( g = 10m/s2, √ 2 = 1.414)

Answer 1

Answer:

Correct option is

B

31.25 m

Height of the building is given by 2nd equation of motion,

S=ut+

2

1

gt

2

now since initial velocity is zero so 2nd equation of motion, become,

S=

2

1

gt

2

=

2

1

×10×2.5

2

=31.25m

Answer 2

Answer:

velocity of object when strike the earth = √2gh

= √2×10×250= 70m/s

time to fall = S=1/2gt^2

250×2/10=t^2

t=√50 =7 sec