Question

If there is no air resistance, a quarter dropped from the top of New York’s Empire State Building would reach the ground 9.6 s later. (a) What would its speed be just before it hits the ground? (b) How high is the building?

Answer 1

Initial velocity is zero. so u=0

a) From equation of kinematics we know that v = u + at

Where v = final velocity

u = initial velocity = 0m/s

a = gravitational acceleration = -g = -9.81 m/s²

t = time taken = 9.6 seconds

v= u -gt = 0 - 9.81 x 9.6 = -94.176 m/s

Hence the speed just before hitting the ground is 94.176 m/s

b) Height can be determined by the equation

H = ut - 0.5gt²

= 0 - 0.5 x 9.81 x 9.6² = 452.044 m

Hence the height of the building is 452.044 m