Question

On a certain planet, if an object takes 5 seconds to come down to a distance of 5m,then what will be the gravitation force on that planet??

Answer 1

Time taken, t = 5 seconds
Displacement, s = 5 metres
Initial velocity, u = 0 metres/second
Let the acceleration be a m/s2.
When the acceleration is constant, initial velocity, acceleration, time taken and displacement are related by a simple formula:
s=ut+(1/2)at2s=ut+(1/2)at2
Therefore,
5=(0)(5)+(1/2)(a)(52)5=(0)(5)+(1/2)(a)(52)
a×(25/2)=5a×(25/2)=5
a=5/(25/2)a=5/(25/2)
a=10/25a=10/25
a=2/5a=2/5
a=0.4a=0.4
Therefore, the acceleration is 0.4m/s20.4m/s2.
This is the acceleration due to gravity on that planet.
Please note that you can't call ‘acceleration due to gravity’ as ‘gravity’.
Gravity refers to gravitational force. Gravitational force (gravity) due to the planet on any mass ‘m’ (expressed in kilograms) = (0.4×m)(0.4×m)newtons.

.... OR....

S=ut + 1/2 * (at^2)
u=0
so
5 = (a*5*5)/2
So
a= 10/25
a= 0.4 m/s^2.