How do you calculate how dense the Earth is? I keep trying but I get 3.51*10¹⁰kg/m³. I don't know how or where I'm going wrong.

a roller coaster car filled with passengers has a mass of 4.80 kg. what speed must it have at the top of the 7.5 m tall circular loop so the car doesn't fall off?

How do you express a major axis with a length of 2.992x10¹¹m in AU?

You are asked to design a rollercoaster. It will have ten attached cars, each of which will have a mass of 500 kg and carry six people with average mass of 70.0 kg. You want to design a vertical circular loop with a radius of 55.0 m. The centre of the circle would have a height of 71.0 m above the ground.

A cyclist exerts a force of 125 N to accelerate from rest to a speed of 10.0 m/s. What is the cyclist’s power output? Consider the difference between average velocity and instantaneous velocity. 

a rabbit running at 12m/s runs past a dog who immediately gives chase. if the dog accelerates at 2.40m/s^2 and both run in a straight line, how long til the dog catches the rabbit?

Find the displacement of a soccer player who runs 15 m [15° N of E] and then 13 m [5° W of N].

A textbook with a mass of 2.18 kg is pulled across a table with a horizontal force of 5.5 N [E]. If the table has a coefficient of friction of 0.15, what is the acceleration of the textbook?

A 37.8 kg child is standing on a scale in an elevator.Determine the reading on the scale if the elevator is accelerating upwards at 4.1om/s^2