Question 38
A boy throws a stone with a horizontal velocity of 10 m s-1 from the top of a building. The height of the building is 8.0 m. The stone travels along a curved path until it hits the ground, as shown in the diagram.
How long does it take the stone to reach the ground? (Air resistance can be neglected.)
A 0.61 s B 0.80 s C 1.3 s D 1.6 s
Reference: Past Exam Paper – November 2015 Paper 13 Q9
Solution:
Answer: C.
Since the stone is thrown horizontally, its vertical component of initial velocity is zero.
Consider the vertical motion.
Initial velocity, u = 0
Distance, s = 8.0 m
Acceleration, a = 9.81 m s-2
Time, t = ???
Consider the equation of uniformly accelerated motion.
s = ut + ½ at2
8 = 0 + ½ × 9.81 × t2
Time t = √(2×8 / 9.81) = 1.27 s
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