Motion and forces — Intermediate

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Level 2: Intermediate

Explain, apply, analyse, sequence — connect ideas, read patterns, use rules in new contexts (bridge to Year 11).

1. A 450 N net horizontal force produces 2.5 m/s² on a crate. The crate’s mass is:

   A)1125 kgB)180 kgC)225 kgD)18 kg

2. You push a heavy shopping trolley and it barely accelerates. $F_{\text{net}} = ma$ on the trolley is still consistent because:

   A)The applied push is the net force, so a small acceleration means the trolley’s mass must be negligibleB)If acceleration is small, $F_{\text{net}}$ must exceed $ma$ until motion startsC)Friction is not a force on the trolley once you are pushing, so $F_{\text{net}}$ equals your push aloneD)The net force on the trolley may be small if friction and other forces nearly balance your push

3. A book rests on a table. Weight pulls the book down and the table exerts an upward normal force. For a stationary book, these forces on the book:

   A)Are a third-law pairB)Balance to give zero net force on the book (first law equilibrium)C)Sum vectorially to the book’s weight plus the normal force, giving a downward net forceD)Act on different bodies, so the book cannot be in equilibrium

4. Why do action–reaction partners not cancel when finding the net force on one object?

   A)They have different magnitudes whenever surfaces are horizontalB)Only one partner should be drawn on a free-body diagram, so the other is ignored by definitionC)They act on different bodies; net force sums forces on the chosen object onlyD)They always point in the same direction, so they add rather than cancel

5. A 2.0 kg object accelerates at 6.0 m/s². The net force is:

   A)12 NB)8 NC)3 ND)0.33 N

6. A 5.0 kg block slides with constant speed on a rough horizontal floor. The horizontal net force on the block is best described as:

   A)Equal to the block’s weightB)Equal to kinetic friction only, always larger than the applied pushC)Zero if speed is truly constant (horizontal forces balance)D)Non-zero because moving objects always have net force in the direction of motion

7. Two forces on one object: 12 N east and 5 N west on the same line. The magnitude of the net force is:

   A)17 NB)7 NC)60 ND)2.4 N

8. A rocket expels gas backward. The rocket accelerates forward partly because:

   A)The gas pushes Earth, which pushes the rocket through the groundB)Third-law partners on the rocket add to give extra net forceC)Mass decreases so F = ma forces acceleration even when thrust is zeroD)The rocket pushes gas backward; the gas pushes the rocket forward (interaction pair)

9. On Earth, weight is most closely related to:

   A)Gravitational force on the object (often W = mg near the surface)B)Normal force from any surface the object touchesC)The object’s inertia measured in kilogramsD)The net force whenever the object is at rest

10. A person stands in a lift accelerating upward. Compared with standing on solid ground, the normal force from the floor on the person is:

    A)Always equal to mg regardless of accelerationB)Larger than mg (apparent weight increases)C)Smaller than mg alwaysD)Zero because the lift is not an inertial frame

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