Work, Energy and Power

What is the definition of work done on a system?

• Force exerted and the object moves in the opposite direction

• Product of force and displacement of object in the direction of the force

• A man pushed a wall and the wall did not moves

• Work done and cause the energy out from the system

These are the unit for work done except

• kg m² s^-2

• Joule

• Newton meter

• Nm^-2

A force of 20 N is used to pull this box to the left for a distance of 100 m. What is the value of work done on the box?

• 1300.6 Joule

• 1519.4 Joule

• 2000.0 Joule

• 30 000 Joule

Choose the correct statement

• Gravitational potential energy is energy due to its position from the ground level

• Energy is the work done in unit Newton

• Kinetic energy is the capacity of work done on an object

• Energy can only be transferred out from the object

A picture of a plane of mass 80 000 kg is flying in the air at velocity of 900 kmh^-1. The height of the planes is 35 000 feet from the ground level.

Calculate it gravitational energy and kinetic energy at that time.

• PE = 2.74 x 10¹⁰ J, KE = 2.50 x 10⁹ J

• PE = 2.74 x 10¹⁰ J, KE = 3.24 x 10¹⁰ J

• PE = 8.37 x 10⁹ J, KE = 3.24 x 10¹⁰ J

• PE = 8.37 x 10⁹ J, KE = 2.50 x 10⁹ J

What is the principle of conservation of energy principle?

• energy can be created and destroyed. Energy can be transferred from one another

• energy can be created but it cannot be destroyed. Energy can be transferred from one another.

• Energy can be transferred from other forms and other object. Energy cannot be created or destroyed.

• Total energy for the system is not constant, It will depends on the value of gravitational energy and kinetic energy.

There are FOUR kids climbing the ladders. Given are their details of mass, height they climbed and the time they took.

Kid A = mass of 20 kg, height, h = 10 m, time, t = 60 s

Kid B = mass of 25 kg, height, h = 7 m, time, t = 30 s

Kid C = mass of 30 kg, height, h = 3 m, time, t = 20 s

Kid c = mass of 25kg, height, h = 0 m, time, t = 0 s

Which one of them have the highest body power of all?

• Kid A

• Kid B

• Kid C

• Kid D

A fan of power of 80 Watt has mass of the blades and motor of 1.2 kg. The fan blades moves at 18 ms^-1 in 45 seconds. Find the efficiency of the fan.

• 5.4 %

• 5.9 %

• 54 %

• 59 %

A machine is used to raise a mass of 250 kg to a height of 17 m within 15 seconds.

Calculate the power of the machine.

A 2 kg of mass was dropped from a height. If its maximum kinetic energy before it stroked the ground is 400 Joule, calculate its height dropped.