Shoot The Monkey...

Classical Mechanics Level 2

This is a heritage physics thought experiment.

Imagine a vet with a tranquilizer gun in the jungle who has just spotted a diseased monkey grasping a tree branch above him. The vet must capture the monkey to treat it for a disease before releasing it back into the wild.

The vet also knows that the monkey will reflexively drop from the branch immediately after he pulls the trigger of his tranquilizer gun.

Where should the vet aim? Where would you aim?

Remember the monkey will free fall to the ground the instant you pull the trigger...

Above the Monkey Doesnt matter Below the Monkey Directly at Monkey

Satyen Nabar by Satyen Nabar , 48, India

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7 solutions

Satyen Nabar
Aug 29, 2014

Aim directly at the monkey.

Once the bullet exits the gun, there’s only one force acting on it with any significance: gravity. Likewise, only gravity will act upon the monkey after he loosens his grasp.

The constant acceleration due to gravity affects both the monkey and the tranquilizer in the same way. Consequently, the bullet will fall a little bit below the initial aim trajectory. By the time the bullet travels the horizontal distance to reach the branch, the monkey will have fallen the same amount as the bullet in the vertical direction, leading to impact.

The speed of the bullet doesn’t even matter in this case. A faster bullet will hit the monkey at a higher height while a slower bullet will simply meet the monkey closer to the ground.

34 Helpful 1 Interesting 2 Brilliant 1 Confused

Classic case of relative motion

Nanayaranaraknas Vahdam - 6 years, 9 months ago

What about the weight? Weight of bullet would be negligible when compared to the Monkey.

Arjunesh Namboothiri - 6 years, 6 months ago

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Weight of the bullet is negligible. True. But acceleration of the bullet is the same as the acceleration of the monkey, which is equal to the acceleration due to gravity, 9.8m s^-2.

Dhruv Bhanushali - 6 years, 2 months ago

@Arjunesh Namboothiri , accleration due to gravity (m/s^2) is independent of mass. Air drag is not given. Hence, both will fall at same rate.

Hari Kumar - 2 years, 1 month ago

the drift taken by the bullet=dist travelled by the monkey

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problem didn't say the monkey was required to be tranquilized. Shoot gun and it will drop no matter what. Doesn't matter where you shoot. Catch monkey when it falls by standing directly under it :)

Noost King - 6 years, 9 months ago

but the monkey has to be captured! it will fall down no matter what!

Srinag Rao - 6 years, 9 months ago
Sean Henderson
Nov 13, 2014

The monkey is above the vet, so just aim straight at the monkey. The tranquilizer dart will travel straight up and the monkey will fall straight down, making the collision of the two (and hence the successful tranquilization of said monkey) happen even faster. No need to consider angles, horizontal velocity, etc. as the monkey is, admittedly, above the vet. The only things that need considered are vertical components.

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Chirag Shetty
Oct 10, 2014

Write a solution. because in the motion of both of them the effect of acceleration due to gravity will compensate each other

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Lakshay Sethi
Sep 10, 2014

Aim directly at the monkey because as when we shoot the tranquilizer the dart will move up. But when we resolve this velocity of projection into components we will get a vertical velocity component and a horizontal one. As there is no force acting in horizontal direction (ignoring air resistance) horizontal velocity will remain constant. But for vertical velocity gravity will act. If we ignore gravity then our dart would reach exactly where the monkey was on the branch. But as gravity cannot be ignored and as it acts equally on monkey and the dart,so the dart should be aimed directly at monkey.

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Sam Tumlad
Aug 31, 2014

Simple PROJECTILE MOTION...

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Represents the classic experiment performed by Galileo, involves dropping two objects simultaneously, assuming negligible air drag . Here two objects are monkey and vet

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