A rock falls from a cliff 6.0 metres above the ground. The mass of the rock is 400 g. Assume air resistance is negligible. Take g = 9.8 m/s 2 . (a) How long will it take for the rock to hit the ground? (b) What will the magnitude of the velocity of the rock be just before it hits the ground? (c) When the rock has fallen 2.0 m from the branch is it in dynamic equilibrium? Assume the rock is now stationary on the ground. A dog 20 m away is running towards the rock with a constant velocity of 4.0 m/s. (d) How long would he need to run before reaching the rock? At 10.0 m from the rock, he hears his owner whistle and decelerates at 4.0 m/s2 , eventually coming to a stop. (e) Describe the change in acceleration that occurs at hearing the whistle. (f) How far is the dog from the rock once he has stopped?