An electric heater takes 1.2kwh in 30min at 120V having an efficiency of 99%.The heat energy required boil a certain amount of water is 99KJ. If the current taken by heater is 20 amp at 120V. Find the time required to boil water?

Two particles of masses m and 2m are placed on a smooth horizontal table. a string, which joins these two masses, hangs over the edge supporting a pulley, which suspends a particle of mass 3m.the pulley has negligible mass. the two parts of the string on the table are parallel and perpendicular to the edge of the table. the hanging parts of the string are vertical. find the acceleration of the particle of mass 3m.

How would doubling the made of an object change the objects potential energy

What is the final velocity of the initial velocity of 25 and -50?