Mechanics and Materials

• What do scalars describe?

  Only a magnitude
• What do vectors describe?

  Magnitude and direction
• When should you use calculation to add vectors?

  When the vectors are perpendicular
• What is the resultant force of two perpendicular forces of 5 N and 12 N?

  $13 N$
• How do you find the direction of a resultant vector?

  Using trigonometry
• What is the formula for finding the direction of a vector?

  $\tan \theta =$$\frac{5}{12}$
• What signifies the direction of the angle found?

  It indicates the vector's direction
• When should you use a scale drawing to add vectors?

  When vectors are at angles other than 90°
• How do you find the magnitude and direction of a ship's displacement?

  By drawing a scale diagram
• What is the condition for an object to be stable?

  Line of action falls within its base
• What happens if the line of action of weight falls outside the base?

  The object will topple over
• What characterizes stable objects?

  Low centre of mass and wide base
• What is the opposite of adding two vectors?

  Resolving vectors
• Why is resolving vectors useful?

  Perpendicular vectors don't affect each other
• What are the formulas to resolve vector V into components x and y?

  $x =$$V \cos \theta, y =$$V \sin \theta$
• What hint helps remember which function to use for resolving vectors?

  Use cos for moving through angle
• What are the vertical and horizontal components of a ball fired at 10 m/s at 30°?

  $x =$$8.7 m/s, y =$$5 m/s$

  
• How do you find the components of weight on an inclined plane?

  Using trigonometry
• What is the formula for the parallel component of weight on an incline?

  $50 \sin 15°$
• What is the value of the parallel component of weight on an incline?

  12.9 N
• What is the formula for the perpendicular component of weight on an incline?

  $50 \cos 15°$
• What is the value of the perpendicular component of weight on an incline?

  48.3 N
• What must be true for an object to be in equilibrium?

  Sum of all forces must be zero
• How can you show an object is in equilibrium?

  • Add horizontal and vertical components of forces
  • Draw a scale diagram forming a closed triangle
• What is the formula for the moment of a force about a point?

  Moment = Force × Perpendicular distance
• What is a couple in physics?

  A pair of equal and opposite forces
• How do you find the moment of a couple?

  Multiply one force by the distance
• What does the principle of moments state?

  Sum of anticlockwise moments equals clockwise moments
• How do you find the value of F using moments?

  Set clockwise moments equal to anticlockwise moments
• What is the definition of the centre of mass?

  Point where an object's mass acts
• Where is the centre of mass in a uniform object?

  Exactly at its centre
• What is speed in physics?

  A scalar quantity describing travel rate
• What is displacement?

  Overall distance travelled with direction
• What is velocity?

  Rate of change of displacement
• What is acceleration?

  Rate of change of velocity
• How is instantaneous velocity found from a graph?

  By drawing a tangent and calculating gradient

  
• How is average velocity calculated?

  Final displacement divided by time taken
• What is uniform acceleration?

  Constant acceleration of an object
• What do acceleration-time graphs represent?

  Change in acceleration over time

  
• What do velocity-time graphs represent?

  Change in velocity over time