A student accidentally drops her keys from rest from a balcony above the ground

PHYSICS · Single correct · A Level · Physics · Mechanics and materials · Mechanics and materials

Problem

A student accidentally drops her keys from rest from a balcony

50\,\text{m}

above the ground. Exactly

1.0\,\text{s}

after the keys are released, she throws a rock straight downward from the same point with a speed of

15\,\text{m}\!\cdot\!\text{s}^{-1}

. Neglect air resistance. At what time after the keys are released does the rock catch up to the keys? (a)

1.33\,\text{s}

(b)

3.0\,\text{s}

(c)

2.0\,\text{s}

(d)

1.6\,\text{s}