A stone is dropped from rest from the top of a 45 m high tower. At the same instant, another stone is projected vertically upward from the ground with a speed of 30 m/s. Neglect air resistance and take g = 10 m/ $s^2.$ After what time do the two stones meet?
Options

Question

A stone is dropped from rest from the top of a 45 m high tower. At the same instant, another stone is projected vertically upward from the ground with a speed of 30 m/s. Neglect air resistance and take g = 10 m/ $s^2.$ After what time do the two stones meet?

Options

G1 Physics · Accepted Answer

Taking upward as positive from the ground, the lower stone has position y1 = 30t - 5t^2. The upper stone has position y2 = 45 - 5t^2. At meeting, y1 = y2, so 30t - 5t^2 = 45 - 5t^2, giving 30t = 45 and t = 1.5 s. Hence, option B is correct.

A stone is dropped from rest from the top of a 45 m high tower. At the same instant, another stone is projected vertically upward from the ground with a speed of 30 m/s. Neglect air resistance and take g = 10 m/s^2. After what time do the two stones meet?