Question

某人以20米每秒的初速度竖直向上抛一石块，石块运动到离抛出点15米处所经历时间为多少

Answer 1

一.∵VB=40m/s,g=10m/s^2, h1=1/2gt^2=5t^2,h2=40t-1/2×10t^2=40t-5t^2,h1+h2=80m=40t-5t^2+5t^2,∴t=2S
二.h2=40m/s×2S-5m/s^2×2S^2=60m
三.A在做与B相向的加速运动

Answer 2

v0t-0.5gt^2=h
20t-0.5*10*t^2=15
t=1 or 3 (s)