HUNT DOWN THAT DEER!!!!!!!!!!

Classical Mechanics Level 2

A Hunter is riding an elephant of height 4m moving in a straight line with uniform speed of 2m/sec.A deer running with a speed V in front at a distance of 8.94427m is moving perpendicular to the direction of motion of elephant.If the Hunter can throw his spear with a speed of 10m/sec relative to the elephant at an angle 'A' to its direction of motion for a successful hit....find the speed V of the deer to the nearest integer


The answer is 6.

Shikhar Jaiswal by Shikhar Jaiswal , 23, India

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2 solutions

Anubhav Tyagi
Sep 13, 2016

Good Question Buddy.. Great way to start on brilliant

2 Helpful 0 Interesting 0 Brilliant 0 Confused

Here,you had to add your solution and not comment on anybody's question.

Manya Singh - 2 years, 11 months ago
Ayush Anand
Apr 14, 2018

This problem could be solved by using coordinate geometry.

Consider the above diagram. Here the chord represents the trajectory of deer wrt elephant and the circle is the locus of all points where the spear could strike.

to calculate the radius of this circle we can use the following equations

(1/2) g (t^2)=4

=> t=2/sqrt(5)

now the radius of the circle will be 10 t=4 sqrt(5) which is same as the horizontal distance between deer and elephant initially.

Now by eqn of circle x^2+y^2=80--(1) by eqn of line => y=(2/v) x+4 sqrt(5)--(2) here 2/v=cot(alpha) which is the slope of deer trajectory wrt elephant. also x=-v*2/sqrt(5)--(3)

substituting (3) in (2) we get y as 16/sqrt(5)

substituting this in (1) we get x^2=(400-(16)^2)/5 again using (3) we get (4/5) v^2=4 (36)/5

=> [v=6]

1 Helpful 1 Interesting 1 Brilliant 2 Confused

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