Physics O Level: Work, Energy, Power and Efficiency PART 1

Kinetic energy of a moving car equals to:

• (1/2) X (mass of the car) X (velocity of the car)²

• (1/2) X (mass of the Earth) X (velocity of the Earth)²

• (1/2) X (mass of the road) X (velocity of the road)²

• (1/2) X (mass of the wind) X (velocity of the wind)²

Gravitational potential energy of a ball on a cliff equals to:

There are two correct answers.

• (mass of the ball) X (height of the cliff)

• (weight of the ball in Newton) X (height of the cliff)

• (mass of the cliff) X (gravitational field strength on Earth) X (height of the cliff)

• (mass of the ball) X (gravitational field strength on Earth) X (height of the cliff)

A ball is on top of a cliff. The gravitational field strength is 10N/kg. What is its total gravitational potential energy when it is at the top of the cliff.

• 1000Joules

• 10 000Joules

• 100Joules

• 10Joules

At the top of the cliff, the ball has gravitational potential energy of 10 000joules. After a fall, at the bottom of the cliff, all of these potential energy has changed to kinetic energy. What is the velocity of the ball just before it hits the sea? which formula would you use?

• 2 X 10kg X velocity² = 10 000joules

• 1/2 X 10kg / velocity² = 10 000joules

• 1/2 X 10kg X velocity = 10 000joules

• 1/2 + 10kg X velocity² = 10 000Joules

Each side of the weight bar is 40 kg. what is its total MASS?

• 40kg

• 20kg

• 80kg

• 100kg

Given the gravitational field strength is 10N/kg, what is the total WEIGHT of the bar weight?

• 400N

• 800N

• 200N

• 1600N

Given the gravitational field strength is 10N/kg, what is the total WORK DONE by the weight lifter?

• 800N x 1.2m = 960Joules

• 800N x 0.6m = 480Joules

• 400N x 0.6m = 240Joules

• 400N x 1.2m = 480Joules

Given the gravitational field strength is 10N/kg, the total work done by the weight lifter is 960 joules.

The weight lifter takes 5 seconds to lift the weight bar.

How would you quantify how powerful he is? (what is his POWER rating).

• 960J / 5s = 192Watts

• 5s / 960J = 0.0052Watts

• 960J x 5s = 4800Watts

• 960J / 10s = 96Watts