Need help in 2D collision problem

A projectile proton with a speed of 200 m/s collides elastically with a target proton initially at rest. The two protons then move along perpendicular paths, with the projectile path deviating by 60∘ from its original direction. After the collision, what is the approximate speed of the target proton?

Please help me.. I have no idea at all.. What i think is the speed become 200 cos60.. But, it says that the correct answer is 170 which is approximate to 200sin60... Please explain me how to solve the problem step by step

#Mechanics

Easy Math Editor

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Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$