A horizontal bridge is built across a river. A student standing on the bridge throws a small ball vertically upwards with a velocity 4 m s⁻¹. The ball strikes the water surface after 4 s. The height of the bridge above the water surface is: (Take g = 10 m s⁻²)
Options

Question

A horizontal bridge is built across a river. A student standing on the bridge throws a small ball vertically upwards with a velocity 4 m s⁻¹. The ball strikes the water surface after 4 s. The height of the bridge above the water surface is: (Take g = 10 m s⁻²)

Options

G1 Physics · Accepted Answer

Step 1: Take upward as positive. The displacement after 4 s is y = ut − ½gt² = 4×4 − ½×10×16 = 16−80 = −64 m. Step 2: The negative sign means the water surface is 64 m below the point of projection. Final answer: A.