Energy, Work Done, Power and Efficiency - Physics Test C8

Rank in order, from largest to smallest, the gravitational potential energies of the balls.

• 1 > 2 = 4 > 3

• 1 > 2 > 3 > 4

• 3 > 2 = 4 > 1

• 3 > 2 > 4 > 1

Two identical marbles roll down two differemt hills. One rolls down a steeper hill, and the other down a less steep hill. Both hills have the same height. How do you compare the change in Gravitational Potential Enrgy (G.P.E.) for the marbles?

• Smaller change in G.P.E. for the steeper hill

• Bigger change in G.P.E. for the less steep hill

• Same change in G.P.E. for both hills

• Can’t say without knowing the mass of the marble

A small child slides down each of the four frictionless slides in the picture. All slides A to D have the SAME HEIGHT. Rank her speeds at the bottom of each slide.

• vD > vA > vB > vC

• vD > vA = vB > vC

• vC > vA > vB > vD

• vA = vB = vC = vD

What is the equation used to calculate Kinetic Energy?

• K = m . v²

• K = m . v

• K = 1/2 . m . v²

• K = 1/2 . (m . v)²

What is the equation used to calculate Gravitational Potential Energy?

• U_g = m . g . h

• U_g = m . g

• U_g = 1/2 . k . x²

• U_g = m . v²

What is the equation used to calculate Work?

• W = m . v

• W = F . d

• W = F / d

• W = m . v²

What is stated by the Law of Conservation of Energy?

• Energy cannot be created or destroyed, but it can change from one form to another.

• The energy of a system will increase over tiime.

• The energy of a system will decrease over time.

• Energy is only conserved in the absence of friction.

The picture shows a skier taking part in a downhill race.

Her mass, including her equipment, is 75 kg. In the ski race, the total vertical change in height is 880 m.

Calculate the decrease in gravitational potential energy of the skier.

(Use g = 10 N/kg)

• 750 J

• 660,000 J

• 66,000 J

• 33,000 J

A man lifts three boxes together from the ground on to a shelf that is 1.5 m above the ground. The weight of the boxes is 300 N and the man takes 2.0 s to lift them.

How muck power does the man produce to lift the boxes?

• 75 W

• 225 W

• 300 W

• 900 W

A skier walks from the bottom of a ski slope to the top and gains 10000J of gravitational potential energy. She skis down the slope. At the bottom of the slope, her kinetic energy is 2000J. How much energy is dissipated in overcoming friction and air resistance as the skier moves down the slope?

• 2000J

• 8000J

• 10 000J

• 12 000J