一、Linear motion 1 (直线运动1）1. An object is travelling with a speed of 4.2m/s in an Easterly direction on a straight road ,It changes its speed to 8.60m/s in 4.00s,calculate the magnitude of its acceleration.(一个物体在4秒内速度有4.2米每秒变为8.60米每秒，求加速度）2. An object starts from rest and accelerates at a uniform rate of 2.40m/s until it reaches a speed of 38.4m/s.(一个物体以2.40的加速度从0加速到38.4米每秒）(a) calculate the time required to reach 38.4m/s.（计算所用时间）(b) draw a velocity-time graph of the motion during
