Chapter 6

A mass m is situated in a uniform gravitational field. When the mass moves through a displacement x, from P to Q, it loses an amount of potential energy E. Which row correctly specifies the magnitude and the direction of the acceleration due to gravity in this field?

• A

• B

• C

• D

A mass at point X inside a uniform gravitational field experiences a gravitational force of 0.200 N. It has 1.00 J of gravitational potential energy. The mass is then moved to point Y.

What is its new gravitational potential energy?

• 0.90 J

• 0.94 J

• 1.06 J

• 1.10 J

A trolley starts from rest at X. It rolls down to Y and eventually comes to rest at Z.

Which row is a possible summary of the energy changes during this process?

• X to Y: PE → KE

  Y to Z: KE → PE

• X to Y: PE → KE

  Y to Z: KE → PE + heat

• X to Y: PE → KE + heat

  Y to Z: KE → PE

• X to Y: PE → KE + heat

  Y to Z: KE → PE + heat

A parachutist is falling at constant (terminal) velocity.

Which statement is not correct?

• Potential energy is converted into kinetic energy of the air.

• Potential energy is converted into kinetic energy of the parachutist.

• Potential energy is converted into thermal energy of the air.

• Potential energy is converted into thermal energy of the parachutist.

A uniform solid block has weight 500 N, width 0.4 m and height 0.6 m. The block rests on the edge of a step of depth 0.8 m, as shown. The block is knocked over the edge of the step and rotates through 90° before coming to rest with the 0.6 m edge horizontal.

What is the change in gravitational potential energy of the block?

• 300 J

• 400 J

• 450 J

• 500 J

A box of weight 30 N is released from rest on a ramp that is 30° to the horizontal. The box slides down and falls through a vertical distance of 8.0 m. A constant frictional force of 10 N acts on the box.

What is the kinetic energy of the box after falling through this distance?

• 80 J

• 160 J

• 240 J

• 400 J

A projectile is launched at 45° to the horizontal with initial kinetic energy E. Assuming air resistance to be negligible, what will be the kinetic energy of the projectile when it reaches its highest point?

• 0.50 E

• 0.71 E

• 0.87 E

• E

The power P required to move an object through a medium at constant speed depends on the speed v and the resistive force F acting on the object. The resistive force F also depends on the speed v. Which row shows a possible relationship between speed v, resistive force F and power P ?

• A

• B

• C

• D

A combined heat and power (CHP) station generates electrical power and useful heat. What is the efficiency of the CHP station for producing useful power?

• 31 %

• 38 %

• 50 %

• 81 %

Some gas in a cylinder is supplied with thermal energy q. The gas does useful work in expanding at constant pressure p from volume V₀ to volume V_F. Which expression gives the efficiency?

• (p V₀) / q

• V_F / (V₀ q)

• p(V_F - V₀) / q

• (V_F - V₀) / (V₀ q)