The height of a rocket above t seconds after firing is given by s=ut-5t^2, where u represents the initial speed of the rocket. If the initial speed is 70 ms^-1, find the amount of time the rocket is in the air and the time the rocket is above 30m.

Ametal ball with a mass of 0.028 kg is dropped from rest at a height of 1.0 meters above the ground. assuming the energy in the ball is conserved, how much kinetic energy will the ball have when it is 0.5 meters above the ground?

Which body part transports oxygen removes waste materials in carries nutrients to the body as part of the circulatory system

Aresistor with an unknown resistance is connected in parallel to a 9 ω resistor. when both resistors are connected in parallel to an emf source of 21 v, the current through the unknown resistor is measured with an ammeter to be 4 a. what is the resistance of the unknown resistor? answer in units of ω.