A shore radar observes a ferry moving at 10 m s⁻¹ at 30° north of east. Ferry instruments show its velocity relative to river is 10 m s⁻¹ at 30° north of west. Find river speed in m s⁻¹, nearest integer.
Physics · Kinematics part-3 Relative motion · River problem
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Question

A shore radar observes a ferry moving at 10 m s⁻¹ at 30° north of east. Ferry instruments show its velocity relative to river is 10 m s⁻¹ at 30° north of west. Find river speed in m s⁻¹, nearest integer.

Physics · Kinematics part-3 Relative motion · River problem

G1 Physics · Accepted Answer

vriver=vground-boat velocity relative to river. The north components cancel and east components add: vriver=20cos30°=10√3≈17.32 m s⁻¹. Nearest integer=17.