what is the work to be done to increase the velocity of a car from 30 km h-1 square to 60 km h-1square if the mass of the car is 1500 kg​

What is the role of lenses in microscopy?

The frequency of the fundamental of the guitar string is 320 hz. at what speed v do waves move along that string?

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.