✔ 最佳答案
I believe the answer should be "C" 3E/4.
Since it is projected at 45 degree
initial KE due to horizontal speed = initial KE vertical = 1/2 [1/2 m v^2]
KE (horizontal) + KE (vertical) = KE (overall)
(v is certainly the initial velocity)
KE (horizontal) does not change during the flight,
while KE (vertical) changed to a half at a height "half way up".
so, KE (vertical) becomes 1/2 * 1/2 * 1/2 mv^2
Hence, at half way up:
KE (vertical) = 1/4 E
KE (horizontal) = 1/2 E
KE = (1/4 + 1/2) E = 3E/4