Force, Work, En...

Which of the following statements is correct?

A man of mass 60 kg climbs up a 20 m long stair case to reach the top of a building, which is 10 m high. What is work done by him?

A car running at 25 km/h can be brought to rest by applying brakes at a distance of 0.5 m. If the car is running at 75 km/h, how far will it go before coming to rest, if the braking force remains the same?

A gun fires bullets each of mass 20 g with a speed of 2 km/s. The person firing the gun experiences a recoil force of 800 N. What is the number of bullets fired per second?

A vehicle is moving on a horizontal road at a constant speed of 10 m/s. The engine needs to spend 5 KJ of energy per second. What is the force on the vehicle?

Which of the following remains constant for an isolated system?

An engine pumps out 40 kg of water in one second. The water comes out vertically upwards with a velocity of 3ms^-1. What is the power of engine in kilowatt?

A body of mass M is lowered with acceleration g/2 with the help of a string and through a distance l. What is the work done by the string?