Question

a ball is dropped from a height of 120 meters. it takes 2 seconds for the ball to fall 60 meters, how long before the ball hits the ground?

Answer 1

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Answer 2

Since the ball has been droppede, its initial velocity will be 0 m/s. Now using the equation S=ut+1/2at\(^2\) we will find first the value of a
60=0*2+1/2a*2*2
60=2a
a=30 m/s\(^2\)

Answer 3

Now using this value of a we can calculate the time taken to travel 120 m by the ball.
120=1/2*30*t\(^2\)
8=t\(^2\)
t=2.82 seconds

Answer 4

This question is not very well defined.

@Abhisar is correct in one interpretation, but it does assume that the experiment is taking place on another planet where gravity is much greater than earth.

I agree that 'dropped' generally means that the initial velocity is 0, however, IF the ball had in initial downward velocity, AND we assume that the acceleration is g (i.e. we are on earth) then (taking g as 10m/s for ease of use...)

s=ut+0.5 at^2

60= 2u +5*2^2 allows us to calculate u

then 120 = ut +5 t^2 will give t for the total fall.

( Not saying I am correct- just that the question is a little open to interpretation....)

Answer 5

@MrNood since in question they have given that "it takes 2 seconds for the ball to fall 60 meters" this means that the accelaration is greater than g i.e 9.8 m/s

Answer 6

This question is not very well defined.

@Abhisar is correct in one interpretation, but it does assume that the experiment is taking place on another planet where gravity is much greater than earth.

I agree that 'dropped' generally means that the initial velocity is 0, however, IF the ball had in initial downward velocity, AND we assume that the acceleration is g (i.e. we are on earth) then ( taking g as 10m/s^2)
s=ut+0.5 at^2

60= 2u +5*2^2 allows us to calculate u

then 120 = ut +5 t^2 will give t for the total fall.

( Not saying I am correct- just that the question is a little open to interpretation....)

Answer 7

@Abhisar

As I said above - I do not question your calculation IF the initial velocity is 0

However - the acceleration ON EARTH is g - 9.81m/s^2, so if your assumption is correct then this experiment is NOT taking place on earth.

MY assertion is that IFthe ball had an initial downward velocity then it CAN travel 60m in 2 s under the normal acceleration of gravity.

Answer 8

hmm..i agree u !
@MrNood