PHYSICS QUIZ: WORK, ENERGY AND POWER

A working electric motor takes a current of 1.5A when the p.d. across it is 250V. If its efficiency is 80%, the power output is

• 469.0W
• 300.0W
• 4.8W
• 133.0W

If a pump is capable of lifting 5000kg of water through a vertical height of 60m in 15min, the power of the pump is

• 2.5 x 10⁴Js-1

• 3.3 x 10²Js-1

• 2.5 x 10⁵Js-1

• 3.3 x 10³Js-1

If a cage containing a truck of coal weighing 750kg is raised to a height of 90m in 1 minute, what is the total power expended?

• 11.50 kW
• 12.60 kW
• 11.25 kW
• 12.10 kw

An object of mass 20kg is released from a height of 10 m above the ground level. The kinetic energy of the object just before it hits the ground is .....

• 2000J
• 500J
• 200J
• 4000J

If a pump is capable of lifting 5000 kg of water through a vertical height of 60 m in 15 min, the power of the pump is

• 3.3 x 10²Js-1

• 2.5 x 10⁵Js-1

• 2.5 x 10⁴Js-1

• 3.3 x 10³Js-1

If the force and the velocity on a system are each reduced simultaneously by half, the power of the system is

• doubled
• constant
• reduced to a quarter
• reduced by half

If a body of mass 5kg is thrown vertically upwards with velocity u, at what height will the potential energy equal to the kinetic energy?

• h = U²/g

• h = U²/4g

• h = 2U²/g

• h = U²/2g

A carpenter on top of a roof 20.m high dropped a hammer of mass 1.5kg and it fell freely to the ground. The kinetic energy of the hammer just before hitting the ground is

• 450 J
• 600 J
• 150 J
• 300 J

If 1.2 x 106J of heat energy is given off in 1 sec from a vessel maintained at a temperature gradient of 30km-1, the surface area of the vessel is

• 1.0 x 10²m²

• 9.0 x 10²m²

• 1.0 x 10³m²

• 9.0 x 10⁴m²

An object is moving with a velocity of 5ms-1.At what height must a similar body be situated to have a potential energy equal in value with the kinetic energy of the moving body?

• 1.0m
• 25.0m
• 20.0m
• 1.3m