A calculate the height in m of a cliff if it takes 213 s for...

(a) Calculate the height (in m) of a cliff if it takes 2.13 s for a rock to hit the ground when it is thrown straight up from the cliff with an initial velocity of 8.18 m/s. (b) How long (in s) would it take to reach the ground if it is thrown straight down with the same speed

Transcript

00:01 In this question, you've been told that a rock is thrown vertically upwards from a cliff with the initial velocity of 8 .18 meter per second and it takes 2 .13 second for the rock to hit the ground.

00:11 We need to, in party, we need to calculate the height of the cliff.

00:15 So first of all, we'll draw the diagram for the path of the rock.

00:19 So the rock will first move upwards, then it will reach its maximum height here.

00:27 Then it will start to move downwards.

00:30 And it will reach its initial height at this point then it will move again downwards and it will hit the ground here now we need to find out the height which is at the height of this cliff now we can find out the height by finding out the displacement of the rock so initially rock is here the initial point and the final point of the rock is here so this this distance is the displacement so the height of the cliff is the displacement of the rock so we're going to use the formula s equals to u t plus half 80 square now by convention we will choose upwards to be positive and downwards to be negative so the initial velocity of the rock is upwards so it is positive 8 .18 into the time which is 2 .35 second plus half into xx is minus 9 .81 because you know that gravitational acceleration act vertically downward so g act in this direction so it's going to be negative and again the square of time which is 2 .35 square so this will give us the displacement that is minus 7 .86 meter so s is actually the displacement this displacement s so this negative sign shows the direction is downward of the displacement.

02:17 So we need to find out the height...

Question

(a) Calculate the height (in m) of a cliff if it takes 2.13 s for a rock to hit the ground when it is thrown straight up from the cliff with an initial velocity of 8.18 m/s. (b) How long (in s) would it take to reach the ground if it is thrown straight down with the same speed

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