# Chapter 2 - Describing Motion: Kinematics in One Dimension - General Problems - Page 46: 66

The total time is 5.75 hours and the average speed is 852 km/hr.

#### Work Step by Step

First, we find: $t_1 = \frac{2100}{720} = 2.92 ~hours$ $t_2 = \frac{2800}{990} = 2.83 ~hours$ Next, The total time is: $t_1+t_2 = 2.92 + 2.83 = 5.75 ~hours$ Therefore, the average speed is $\frac{4900 ~km}{5.75~hours} = 852~km/hr$

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