Question

1. A motorcycle begins driving from at rest position. It accelerates at 8 km/hr2 for 20 seconds, then travels at a steady speed for another 20 seconds, all in the same direction. How much distance has it covered since it started driving?

2. An object is dropped from a cliff, the time it takes to hit the ground is 3 seconds. What is the height of the cliff? What is the velocity of the object before it hits the ground?

Answer 1

1.

$$v=v_0+at=0+6.17*10^{-4}*20=0.012\:\rm m/s$$

$$d=d_1+d_2=at_1^2/2+vt_2\\ =6.17*10^{-4}*20^2/2+0.012*20=0.37\:\rm m$$

2.

$$h=gt^2/2=9.81*3^2/2=44\:\rm m$$

$$v=gt=9.81*3=29\:\rm m/s$$