A body falls freely under gravity (g = 9.8ms-2) from a height of 40m on to the top of a platform 0.8m above the ground. Its velocity on reaching the platform is
A
784ms-1
B
80ms-1
C
78.4ms-1
D
39.2ms-1
E
27.7ms-1
Verified Correct Answer: E.
Physical Principles & Numerical Solution
The total distance fallen is s = 40m - 0.8m = 39.2m
u = 0m/s, v = ? , g = 9.8m/s\(^2\)
Using: v\(^2\) = u\(^2\) + 2gs
v\(^2\) = 0 + 2 x 9.8 x 39.2
v\(^2\) = 768.32
v = \(\sqrt{768.32}\) ≈ 27.7m/s.
Source: Myschool Past Questions Archive (Record #29018)