MCQs – Forces (set 1)

A car reaches a maximum speed. The best explanation for the maximum speed is that:

• the engine has a limited speed at which it can run.

• the driving force from the engine is balanced by the weight of the car.

• the engine cannot exceed zero torque.

• the driving force from the engine is balanced by drag and friction.

A model jet aeroplane has a mass of 2.4 kg. Its jet engine provides a thrust of 6.0 N. In the absence of air resistance, its acceleration would be

• 0.40 m·s⁻²

• 2.5 m·s⁻²

• 2400 m·s⁻²

• 34560 m·s⁻²

In question 2, the power available from the model aeroplane’s engine is 0.30 kW. In the absence of air resistance, what would be the aeroplane’s maximum speed?

• 50 m·s⁻¹

• 35 m·s⁻¹

• 20 m·s⁻¹

• 5.0 m·s⁻¹

A racing car is driving around a track. Which of the following statements are true about its movement? (1) The maximum speed depends on the power available. (2) The maximum speed is when the forward force from the engine is in equilibrium with the drag and friction. (3) As fuel is used up, the car has a greater acceleration. (4) The car pushes up against the aerofoil that holds the car to the road.

• (1) and (2) only

• (1), (2) and (3) only

• (2) and (4) only

• All statements are correct

Newton’s First Law states that:

• Every object continues in a state of rest or uniform motion in a straight line, unless it is compelled to change by an external force acting on it.

• Every object continues to move in a straight line regardless of what happens to it.

• A force that is applied parallel to the direction of motion will make an object move in a circle.

• No unbalanced forces can ever act on an object.

An aeroplane is flying at a constant speed in level flight. Which one of the following statements is true?

• The drag, thrust, lift and weight are all equal.

• The drag is less than the thrust and the lift is greater than the weight.

• The thrust is less than the drag and the weight is greater than the lift.

• The lift is equal to the weight and the thrust is equal to the drag.

Which one statement best describes Newton’s Third Law?

• Forces act singly.

• Forces act in pairs, but only on a static body.

• All forces have to add up to zero.

• Forces act in pairs, regardless of equilibrium or acceleration.

As a firework rocket uses its fuel up, it will:

• accelerate at a greater rate.

• remain at a constant velocity.

• slow down.

• remain stationary in the air.

A parachutist falls from an aircraft and reaches a terminal velocity. After a while, he opens his parachute and reaches a new (lower) terminal velocity. Which graph shows how the total air resistance (drag) force acting on him and the parachute varies with time during the fall?

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A trolley being pulled down a runway by a falling mass is a bad way to demonstrate Newton’s Second Law. This is because:

• If the mass of the falling mass is doubled, the acceleration is doubled.

• The maximum possible acceleration is 10 m·s⁻².

• There is friction in the system.

• The mass of the falling mass has to be added to the mass of the trolley.