A bungee jumper falls from a bridge her bungee cord which...

A bungee jumper falls from a bridge. Her bungee cord, which has zero mass, applies zero force when not extended and a force proportional to its extension otherwise. Which three of the following statements are true? a. At the fastest point of her fall, her acceleration is zero. b.At the lowest point of her fall, her velocity is upwards c. At the lowest point of her fall, her velocity is zero d. At the lowest point of her fall, her acceleration is zero e. At the lowest point of her fall, her acceleration is upwards f. At the lowest point of her fall, her velocity is downwards g. At the lowest point of her fall, her acceleration is downwards

Transcript

00:01 Given situation of a bungee jumper.

00:02 So let's suppose this is your bungee rope and initially the man was standing somewhere here.

00:10 When he jumps, what happens? a rope will open fully.

00:15 So the moment when the rope is fully open, this is the moment.

00:19 The man will have gained some speed here, some speed wheel.

00:27 And at this moment of time, only force acting on the man is mg.

00:32 Because bungee rope is not producing any force.

00:36 Bungee rope will produce a force only when it gets a little bit of stretched.

00:41 So at this point there is no stretching.

00:42 This is the full length of the bungee wire or bungee rope.

00:46 So only downward force is acting which is energy.

00:49 So it has already gained some speed and due to kinetic energy, it will now push the bungee rope.

00:55 It will try to stretch the bungee rope.

00:57 So now as the bungee rope will, i'm plotting it.

01:02 It here as the bungee rope will stretch what will happen a force will grow in the bungee rope due to which the force which is acting on the man is not only m g it is the backward force which is which has also started to act and more the stretching more is the backward force so definitely a point will come when this force by the bungee by the bungee rope and the force by the gravity they will become equal and at this time the acceleration will become equal to zero but till this time the speed will increase because till this time there was a net downward force because m g was greater than this before this before this has arrived if you take any instant here here the force which is uh exerted by the bungee is less than mg due to which a net force still exists downwards and whenever the net force is there net acceleration is there and hence the speed is increasing so speed is increasing to this point.

02:08 Now at this point when the forces becomes zero, now the speed will not increase further from here.

02:16 So i would say the speed has become highest here because what will happen after this? after this, bungee force will become more than mg due to which retardation will start and the speed will start to decrease...

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