IGCSE Physics Forces topical questions

Name the effect each force produces.

1. (a)Squeezing a foam ball between your hands[1]
2. (b)A rocket engine firing, changing the rocket’s speed[1]
3. (c)A rudder turning a boat to the left[1]

A book rests on a table. The book’s weight is 4.0 N downwards.

1. (a)State the size and direction of the force the table exerts on the book.[1]
2. (b)State the resultant force on the book.[1]
3. (c)Explain your answer to (b) using Newton’s first law.[1]

A spring is 60 mm long unstretched. With a load of 2.0 N it becomes 66 mm long.

1. (a)State what is meant by the extension of the spring.[1]
2. (b)Calculate the extension with the 2.0 N load.[2]

A student drags a heavy box of books sideways across a carpet. Her pulling force is 40 N and friction from the carpet is 15 N.

1. (a)Work out the resultant force on the box.[1]
2. (b)Describe what happens to the box’s motion.[1]
3. (c)State two effects that friction has as the box slides.[2]

A cyclist and bicycle of total mass 70 kg speed up uniformly from rest to 6.0 m/s in 12 s.

1. (a)Calculate the acceleration.[2]
2. (b)Calculate the resultant force needed, and state its direction.[2]

A student hangs loads from a spring and records the extension. The load–extension graph is a straight line through the origin up to a load of 6.0 N, and curves beyond it.

1. (a)Describe how the student should obtain the readings for the graph.[2]
2. (b)State what the straight section shows about the relationship between load and extension.[1]
3. (c)Name the point at 6.0 N where the line starts to curve.[1]
4. (d)On the straight section, a 2.0 N load gives an extension of 40 mm. Calculate the spring constant.[1]

A wheelbarrow is pivoted at its wheel. A gardener lifts the handles with an upward force 1.2 m from the wheel; the load of 240 N in the bucket acts 0.30 m from the wheel, on the same side.

1. (a)Explain why the gardener’s upward force keeps the barrow level in terms of moments about the wheel.[2]
2. (b)Calculate the lifting force needed.[2]

A car of mass 900 kg is travelling at 15 m/s when the driver brakes. The car comes to a stop in 5.0 s.

1. (a)Calculate the acceleration of the car, stating what the sign of your answer means.[2]
2. (b)Calculate the size of the resultant braking force.[2]

A door is pushed open with a force of 12 N applied to the handle, 0.80 m from the hinges. The force acts perpendicular to the door.

1. (a)State the equation for the moment of a force.[1]
2. (b)Calculate the moment of the push about the hinges.[2]
3. (c)Explain why door handles are placed as far from the hinges as possible.[1]

A uniform metre rule is pivoted at its 50 cm mark. A 4.0 N weight hangs at the 20 cm mark and a 6.0 N weight hangs at the 80 cm mark.

1. (a)Calculate the total anticlockwise moment about the pivot.[2]
2. (b)Calculate the total clockwise moment about the pivot.[2]
3. (c)State and explain which way the rule will start to rotate.[1]

A uniform metre rule of weight 1.2 N is pivoted at its centre. A 3.0 N weight hangs at the 25 cm mark. A student hangs an unknown weight W at the 90 cm mark and the rule balances horizontally.

1. (a)Explain why the rule’s own weight produces no moment about the pivot.[2]
2. (b)Calculate W using the principle of moments.[3]
3. (c)State the value of the resultant force on the balanced rule.[1]

A flat, irregular piece of plywood is to have its centre of gravity found, and then be mounted on a short pole as a sign.

1. (a)Describe how to find the centre of gravity of the plywood by suspension.[3]
2. (b)Explain, using the idea of the line of weight, why the plywood stays put when supported exactly at its centre of gravity.[2]
3. (c)The sign is later mounted on a narrow pole with a heavy lamp fixed to its top. State and explain what happens to its stability.[1]

A uniform metre rule is pivoted at its centre (the 50 cm mark). A weight of 5.0 N hangs at the 20 cm mark and a weight of 4.0 N hangs at the 35 cm mark, both on the left of the pivot.

1. (a)Write down how far each weight sits from the pivot.[1]
2. (b)Calculate the total anticlockwise moment about the pivot.[2]
3. (c)Calculate the weight that must hang at the 85 cm mark to balance the rule.[2]