An object is in motion if its distance relative to another object is changing. To tell if an object is moving, you use a reference point. If an object's distance from another object [reference point] is changing. A place or object used for comparison to determine if something is in motion.
The rock would be at a point 12 m from water at a time <u>4.8 s</u>.
Take the origin of the coordinate system at the top of the cliff. It is thrown upwards with a velocity u. When the rock is at a point 12 m from water, calculate the vertical displacement of the rock from the origin.

Use the equation of motion,

The rock falls under the acceleration due to gravity, directed down wards.
Substitute 18 m/s for u, -26 m for y and -9.8 m/s² for a=g.

Solve the quadratic equation for t.

Taking only the positive value,

After a time of <u>4.8 s</u> the rock would be at a distance of 12 m from water.
Answer:
- your body moving forwards when sudden brakes/force is applied e.g. sudden braking in a car
- feeling a backwards force when something moves quickly from rest e.g a bus
- when you stir a cup of tea, it continues to swirl for a short period of time even though you have stopped
- when shaking a tree, it's leaves or fruit fall down
- satellites which move due to the inertia of motion
hope this helped :)
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