National Certificate of Educational Achievement Ā· Science

Mechanics, Forces, Work, Power, Energy and Wave Systems

39 practice questions, each with the answer and an explanation.

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All 39 questions

  1. What is the net force acting on a 1200 kg car travelling along a straight highway at a constant velocity of 100 km/h?
  2. A crate of mass 40 kg is pushed across a horizontal concrete floor with a horizontal force of 150 N. If a constant frictional force of 70 N opposes the motion, what is the acceleration of the crate?
  3. How much work is done when a student lifts a 15 kg school backpack vertically through a height of 1.2 metres (take g = 10 N/kg)?
  4. A cyclist of total mass 80 kg accelerates from rest to 10 m/s in 4 seconds. What is the average power output of the cyclist over this interval?
  5. A stone is dropped from rest from the edge of a cliff in the South Island and hits the ground after 3.0 seconds. What is the height of the cliff (take g = 10 m/s^2)?
  6. Why does a person wearing snowshoes not sink deeply into fresh powder snow in the Southern Alps, whereas a person in standard boots does?
  7. What type of wave is sound in air, and in what direction do air particles vibrate relative to the wave propagation?
  8. An ocean swell off the coast of Raglan has a wavelength of 30 metres and a frequency of 0.25 Hz. What is the speed of the swell?
  9. When light passes from air into water at an angle, why does the light ray bend toward the normal line?
  10. A skydiver of mass 70 kg jumps from an aircraft over Lake Taupō and reaches terminal velocity. What is the magnitude of the air resistance force acting on the skydiver (take g = 10 N/kg)?
  11. What type of energy transformation occurs when an electric kettle boils water on the stove?
  12. A car of mass 1000 kg traveling at 20 m/s brakes to a complete stop over a distance of 40 metres. What average braking force was exerted on the car?
  13. What property of a musical sound wave determines its perceived pitch?
  14. A ball is thrown horizontally at 15 m/s from the top of a 20 m high cliff. How long does it take to hit the ground (take g = 10 m/s^2)?
  15. What happens to total momentum when two shopping trolleys collide and stick together on a frictionless surface?
  16. Why does a convex lens converge parallel rays of sunlight to a single focal point?
  17. A 0.5 kg roller-coaster cart starts from rest at the top of a frictionless track of height h = 8.0 m. At the bottom of the track, it enters a rough horizontal section of length 10 m with a frictionalā€¦
  18. A 60 kg bungee jumper leaps from the Kawarau Gorge Bridge. When the 20 m elastic bungee cord begins to stretch, the jumper has fallen 20 m freely. What is the jumper's velocity just as the cord beginsā€¦
  19. A sound wave travels from warm air at 25 deg C (speed 346 m/s) into cold air at 0 deg C (speed 331 m/s). If the frequency of the sound is 500 Hz, what happens to its wavelength?
  20. A 1500 kg electric car accelerates uniformly from 10 m/s to 30 m/s over a distance of 100 metres. What net work was done on the car during this acceleration?
  21. A heavy crate of mass 50 kg rests on an inclined wooden ramp angled at 30 degrees to the horizontal. If the crate remains stationary, what is the magnitude of the static friction force acting up the rā€¦
  22. In a hydraulic car hoist in an automotive workshop in Christchurch, a force of 200 N is applied to a small piston of cross-sectional area 0.005 m^2. What maximum weight can be supported by the large pā€¦
  23. A 2.0 kg ball travelling horizontally at 6.0 m/s strikes a vertical brick wall and rebounds in the opposite direction at 4.0 m/s. If the impact lasts 0.05 seconds, what average force was exerted by thā€¦
  24. What is the SI unit of electric potential difference (voltage)?
  25. If a resistor of 15 Ohms is connected across a 30 V direct current battery, what current flows through the circuit?
  26. What happens to the total resistance of an electrical circuit when a second identical resistor is connected in parallel with the first?
  27. Which component of the electromagnetic spectrum has the shortest wavelength and highest photon energy?
  28. Why does thermal energy transfer through a solid copper rod primarily by conduction rather than convection?
  29. What is the frequency of a wave that completes 120 oscillations in 30 seconds?
  30. A person stands 3.0 metres in front of a flat plane mirror. What is the distance between the person and their virtual image?
  31. What type of mirror is used in New Zealand road safety corners to provide a wide field of view at blind driveways?
  32. A spring with a spring constant of k = 200 N/m is compressed by 0.15 metres. How much elastic potential energy is stored in the spring?
  33. Seawater has a density of 1025 kg/m^3. What is the mass of seawater contained in a tank measuring 2.0 m by 1.5 m by 1.0 m?
  34. What optical phenomenon occurs when light travelling in optical glass strikes an air boundary at an angle greater than the critical angle?
  35. Why does the siren of an approaching ambulance sound higher in pitch than when the ambulance drives away (the Doppler effect)?
  36. A net force accelerates a 1200 kg car at 2.5 m/s^2. What is the size of the net force?
  37. A worker pushes a box with a horizontal force of 50 N for 4.0 m along the floor. How much work does the worker do on the box?
  38. A motor does 600 J of work in 3.0 s. What is its power output?
  39. A wave has a frequency of 50 Hz and a wavelength of 0.40 m. What is its speed?

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