Which simple machine is a doorknob?

a lever

a screw

a pulley

a wheel and axle

A hot air balloon is rising upward with a constant speed of 2.50m/s. When the balloon is 3.0 m above the ground, the balloonist drops a compass over the side of the balloon. How much time elapses before the compass hits the ground? PS.

A 3-ohm resistor and a 6-ohm resistor are connected in parallel across a 9-volt battery. Which statement best compares the potential difference across each resistor?

What causes the rider on a roller coaster to experience the + or - g's if gravity always remains the same on earth

A sphere is filled with air. If the volume of the sphere is increasing at a rate of 569 cubic inches per minute, what is the rate, in inches per minute, at which the radius of the sphere is changing when the radius is 4 inches?

Why does Alpha Centauri appear to be yellow-white?

Most of the mass of the Milky Way exists in the form of: a.) starsb.) gasc.) dustd.) dark matter

A 55kg cart is pushed by a force of 225 n. what is the carts acceleration?

F we wanted to compare muscular endurance between a very large person and a very small person, what method would be the best method to use? a. absolute method b. maxing out c. callisthenic method d. fixed percentage of rm method

After creating a question and forming a hypothesis, what is the next step in the scientific method

Roger sees water balloons fall past his window. He notices that each balloon strikes the sidewalk 0.51 s after passing his window. Roger's room is on the second floor, 10 m above the sidewalk.