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AS Mechanics Quiz #3

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  • For a body to be in equilibrium, both resultant force and resultant moment must be zero
    True – Both translational and rotational equilibrium must hold.
  • The net force on an object is found by adding all the acting forces vectorially
    True – Net force = vector sum of all forces.
  • A car that is turning while keeping constant speed has no acceleration
    False – The direction of velocity is changing, so acceleration exists.
  • In projectile motion, the horizontal component of velocity is constant (ignoring air resistance)
    True – Gravity only affects vertical motion.
  • If a particle is moving at constant speed around a circle, the direction of motion is changing
    True – Therefore, the velocity is changing.
  • The equation "v = u + at" can be used when acceleration is changing
    False – It only applies when acceleration is constant.
  • An object moving in a straight line under constant acceleration must have constant speed
    False – Constant acceleration changes speed.
  • In modelling, a "particle" has no size or rotation
    True – It’s a point mass.
  • The scalar quantity equivalent to velocity is displacement
    False – That’s speed, not displacement.
  • The normal reaction force is always vertical
    False – It is perpendicular to the surface, not necessarily vertical.
  • Vertical acceleration in projectile motion is constant
    True – It’s always "9.8 m/s²" downward.
  • Velocity-time graphs can be used to calculate total displacement
    True – By finding the area under the graph.
  • Weight is calculated using the equation "W = mg"
    True – Mass times gravitational field strength.
  • A particle in equilibrium has net force equal to zero
    True – That defines equilibrium.
  • When analysing vertical motion, "u" is often taken as positive if upward motion is assumed
    True – It’s a matter of choosing a sign convention.
  • If an object’s velocity and acceleration are in opposite directions, it is speeding up
    False – It is slowing down (decelerating).
  • A horizontal force on a stationary object will always cause motion
    False – The object might remain stationary if the force is balanced.
  • Newton’s Third Law explains why forces occur in pairs
    True – Action and reaction are equal and opposite.
  • An object in free fall near Earth accelerates at "9.8 m/s²"
    True – That’s standard gravitational acceleration.
  • Displacement can be zero even if distance travelled is not
    True – If an object returns to its starting point, displacement is zero.
  • If an object has constant velocity, no net force acts on it
    True – No acceleration implies no resultant force.
  • The total flight time of a vertically projected object is twice the time taken to reach the highest point
    True – Motion is symmetrical.
  • If no external forces act on a body, its momentum remains constant
    True – This is the principle of conservation of momentum.
  • The time taken to reach maximum height in vertical projection is given by "t = u/g"
    True – When final velocity is 0, rearranging "v = u - gt".
  • A particle under no force moves at constant velocity
    True – Newton’s First Law.
  • The reaction force and weight of an object are always equal
    False – Only if there is no vertical acceleration or incline.
  • Force and mass are inversely proportional if acceleration is constant
    False – With constant acceleration, force and mass are directly proportional.
  • Acceleration is a vector quantity
    True – It has both magnitude and direction.
  • A displacement-time graph with a curved line indicates constant velocity
    False – A curved graph shows changing velocity.
  • A light pulley has no mass and affects the tension equally on both sides
    True – Ideal pulleys are massless and frictionless.
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