汽车以45km/h的速度匀速行驶（1）如汽车以0.6m/s的加速度加速,汽车以45km/h的速度匀速行驶（1）如汽车以0.6m/s的加速度加速,则10s后速度能达到多少?（2）若汽车刹车以0.6m/s的加速度减速,则10s

Question

汽车以45km/h的速度匀速行驶 （1）如汽车以0.6m/s的加速度加速,
汽车以45km/h的速度匀速行驶
（1）如汽车以0.6m/s的加速度加速,则10s后速度能达到多少?
（2）若汽车刹车以0.6m/s的加速度减速,则10s后速度能达到多少?
（3）若汽车刹车以3m/s的加速度减速,则10S后速度为多少?

Answer 1

(1)
v0 = 45km/h = 12.5m/s;
v1 = v0 + a1t = 12.5m/s + 0.6m/s2 × 10s = 12.5m/s + 6m/s = 18.5m/s;
(2)
v2 = v0 + a2t = 12.5m/s + (-0.6m/s2) × 10s = 12.5m/s - 6m/s = 6.5m/s;
(3)
t2 = v0 / a3 = 12.5m/s ÷ 3m/s2 = 25/6s ≈ 4.17s < 10s ;
∴ 车在4.17s时停下,10s后的速度为0.