Relative Velocity Problem: Finding Train Speed from Raindrop Angle

AI Thread Summary
A person on a stationary train observes raindrops falling vertically at 5.0 m/s, but when the train moves, the raindrops appear at a 25° angle. The problem involves using relative velocity equations to determine the train's speed. Initial calculations yielded a speed of 2.16 m/s, while the solution manual states the correct speed is 2.3 m/s. Participants suggest using trigonometry and drawing a right triangle to clarify the relationship between the train's speed and the rain's velocity. The discussion emphasizes the importance of accurately interpreting the angles and components in the problem.
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Homework Statement


A person looking out the window of a stationary train notices that rain drops are falling vertically down at a speed of 5.0 m/s relative to the ground. When the train moves at a constant velocity, the raindrops make an angle of 25° when they move past the window. How fast is the train moving?

Homework Equations


##\vec{v_{AC}} = \vec{v_{AB}} + \vec{v_{BC}}##

The Attempt at a Solution


T = train, R = rain, G = ground
##\vec{v_{TG}} = \vec{v_{TR}} + \vec{v_{RG}}##
##\vec{v_{TG}} = \vec{v_{RG}} - \vec{v_{RT}}##
##v_x = 0~m/s-[(5~m/s)\sin25^{\circ}] = 2.1131~m/s##
##v_y = (-5~m/s) -[(5~m/s)\cos25^{\circ}] = -0.468~m/s##
##\vec{v_{TG}} = \sqrt{(2.1131~m/s)^2 + (-0.468~m/s)^2} = 2.16~m/s##

However, according to the solution manual, the correct answer is 2.3 m/s. Where am I going wrong?
 
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Try drawing a right triangle.

The vertical length is the trains speed.
The horizontal length is the rain drop speed of 5.0.

Which angle are you looking from?
What trig will help you solve it in one quick calculation?
 
RJLiberator said:
Try drawing a right triangle.

The vertical length is the trains speed.
The horizontal length is the rain drop speed of 5.0.

Which angle are you looking from?
What trig will help you solve it in one quick calculation?
What do you mean "the vertical length is the train's speed"? Do you mean horizontal?
 
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