F.4 力學問題(英文)

👨🏻‍🏫 學術台其他 - 科學

henry

2010-03-17 3:21 am

the statements below are the descripitons of cars.

Car A:Itcantravel for 50m in 2s from rest.

CarB :It can accelerate from 20ms^-1to40ms^-1 in4s.

CarC: It can travel for 100m in the 5th second from rest.

Find the accelerations of the car and compare their magnitudes

更新1:

Car B: use equation of motion: v^2 = u^2 + 2a.s 40^2 = 20^2 + 2a(4) i.e. a = 150 m/s2 你在這題目中計錯了,你把時間4s當作位移S.

回答 (1)

天同

2010-03-17 4:33 am

✔ 最佳答案

Car A: use equation of motion: s = ut + (1/2)at^2
50 = (1/2)a(2x2)
hence, a = 25 m/s2

Car B: use equation of motion: v^2 = u^2 + 2a.s
40^2 = 20^2 + 2a(4)
i.e. a = 150 m/s2

Car C: velocity after 4 s from rest = 4a, where a is the acceleration
use equation of motion: s = ut + (1/2)at^2
with u = 4a, s = 100 m, t = 1 s, a = ?
hence, 100 = 4a.(1) + (1/2)a.(1x1)
solve for a gives a = 22.22 m/s2

Accelerations of the cars, in ascending order of magnitude, are Car C, Car A, Car B

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