Resultant forces

The diagram shows a truck travelling along a horizontal road.

The diagram shows the horizontal forces acting on the truck.

Give the resultant horizontal force acting on the truck.

The driver of the truck has to stop because a tree has fallen on the road.

The thinking distance of the driver is 7 m.

The braking distance of the truck is 20 m.

Calculate the stopping distance of the truck.

Give two factors that would affect the braking distance of the truck.

Which of these factors would decrease the driver’s thinking distance?

The diagram shows a submarine at rest underwater.

There are two vertical forces acting on the submarine.

One of the forces is called upthrust.

Give the name of the other force.

Draw two arrows on the diagram to represent the vertical forces acting on the submarine.

State the formula linking pressure, density, gravitational field strength and height.

Calculate the pressure from the water at a point 38 m below the surface of the water.

[density of sea water = 1030 kg/m³]

To rise back to the surface, air is pumped into a storage tank inside the submarine.

Explain how the air exerts pressure on the walls of the storage tank.

The air in the storage tank starts at a pressure of 410 kPa.

As the submarine rises, the air in the storage tank increases in temperature from 2.5C to 18C. The volume of the storage tank remains constant.

Calculate the pressure of the air in the storage tank at 18C.

In 1947, the Railton Mobil Special was the first ground vehicle to achieve a speed of more than 400 miles per hour.

During a test, the vehicle travelled at a speed of 403 miles per hour.

Calculate a speed of 403 miles per hour in metres per second (m / s). [1 mile = 1600 m]

During the test, the vehicle travelled past two markers. The markers were placed a known distance apart.

Describe how these markers could be used to determine the speed of the vehicle.

The diagram shows the vehicle travelling at a constant speed.

One of the horizontal forces acting on the vehicle has been drawn.

Complete the diagram by drawing a labelled arrow for the other horizontal force acting on the vehicle.

A metal spring obeys Hooke’s law.

Sketch a graph to show that the spring obeys Hooke’s law as it is stretched.

You should label both axes with appropriate physical quantities.

Diagram 1 shows an object suspended from a support using a metal spring.

The object is initially at rest.

The object is pulled down and then released.

Diagram 2 shows the forces acting on the object at the instant it is released.

Determine the magnitude and direction of the resultant force acting on the object.

The object has a mass of 0.20 kg.

Calculate the acceleration of the object at the instant it is released.

acceleration =_........ ²

Explain how the magnitude of the acceleration of the object changes, from the instant the object is released until the first time the object returns to its initial resting position.

You should refer to the forces acting on the object in your answer.

The diagram shows the forces acting on a firework at take-off.

Calculate the magnitude of the resultant force on the firework.

State the formula linking resultant force, mass and acceleration.

The mass of the firework is 160 g.

Calculate the acceleration of the firework.

Explain how the acceleration of the firework changes between take‑off and running out of fuel.

You can assume that the thrust force stays the same as the firework burns the fuel.

The firework makes a sound with constant frequency.

As the firework moves upwards, people on the ground notice that the frequency of the sound they hear changes.

This is called the Doppler effect.

Explain how the Doppler effect causes the observed frequency of sound to change for the people on the ground.

Diagram 1 shows a wooden plank balanced horizontally on two supports, A and B.

A block is suspended from the plank between the supports by a cable of negligible weight.

The weight of the block is 260 N.

State the formula linking moment, force and perpendicular distance from the pivot.

By taking moments about support A, calculate force F.

Assume the weight of the plank is negligible.

Explain what will happen to the magnitude of force F if the block is moved towards support B.

The centre of gravity of the block is located at point X.

Draw an arrow on diagram 2 to show the weight of the block.

The block also experiences a force due to the tension in the cable.

Explain why the block remains stationary when it is supported by this tension force.

Explain why the forces acting on the block are not an example of Newton’s third law of motion.

Diagram 1 shows an ice cube floating at rest in a beaker of water.

State the value of the resultant force on the ice cube.

Diagram 2 shows the ice cube pushed down into the water by force X.

The ice cube is at rest in this new position.

State the formula linking pressure difference, height, density and gravitational field strength.

The bottom of the ice cube is 0.041 m below the surface of the water.

The density of water is 1000 kg/m³.

Show that the pressure difference between the bottom of the ice cube and the surface of the water is about 400 Pa.

State the formula linking pressure, force and area.

The area of the base of the ice cube is 0.0017 m².

Calculate the upward force on the bottom of the cube from the water due to the pressure difference.

Explain why the ice cube will accelerate upwards when force X is removed.

A student uses this apparatus to measure the force of repulsion between magnet A and magnet B.

Magnet A is clamped in a fixed position.

Magnet B is resting on a balance.

Give a reason why the two magnets shown in the diagram will repel each other.

Give a reason why the top plate of the balance is not affected by the magnetic fields of the magnets.

Complete the diagram by drawing the shape and direction of the magnetic field pattern between the magnets.

In the position shown, the balance reading is 1.6 N.

Explain how the balance reading will change if magnet A is brought closer to magnet B.

Explain how the balance reading will change if the poles of magnet A are reversed but the distance between the magnets remains constant.

This question is about scalar quantities and vector quantities.

Give a similarity and a difference for scalar quantities and vector quantities.

similarity

difference

The box gives some physical quantities.

Draw a circle around each physical quantity that is a scalar.

The diagram shows four forces acting on an object.

Calculate the size and direction of the resultant force.

Very strong magnets can be made using the element neodymium.

Diagram 1 shows parts of two neodymium magnets, X and Y, when they are held close together.

Diagram 1

A uniform magnetic field is produced in the space between the magnets.

Diagram 1 shows the south pole of magnet X.

Complete diagram 1 by drawing the uniform magnetic field and labelling the pole on magnet Y.

Diagram 2 shows another neodymium magnet being used to lift an iron ball from a table.

The iron ball is shown at the instant it leaves the surface of the table.

Diagram 2

Explain why the iron ball experiences an upward magnetic force.

The iron ball experiences an upward resultant force at the instant shown in diagram 2.

Draw a labelled arrow on diagram 2 to show the weight of the iron ball.

State the formula linking weight, mass and gravitational field strength.

At the instant shown in diagram 2, the resultant force acting on the iron ball is 124 mN and the magnetic force is 165 mN.

Calculate the mass of the iron ball.

Explain why the resultant force acting on the iron ball increases as the iron ball moves towards the magnet.

A glass contains fizzy water.

Bubbles of carbon dioxide form at the bottom of the glass and rise to the surface.

The graph shows the relationship between the volume of a bubble and the pressure of the gas in the bubble.

Describe the relationship shown by the graph.

State the formula linking pressure difference, height, gravitational field strength and density.

The depth of the fizzy water in the glass is 22 cm.

The density of the fizzy water is 1080 kg/m³.

Calculate the pressure difference at the bottom of the glass due to the fizzy water.

Calculate the pressure of the gas in the bubble when the bubble is at the bottom of the glass.

[atmospheric pressure = 101 000 Pa]

When a bubble is at the top of the glass, the pressure of the gas in the bubble is equal to 101 000 Pa and the bubble has a volume of 0.084 cm³.

Calculate the volume of the gas in the bubble when the bubble is at the bottom of the glass.

Assume the temperature of the gas remains constant.

volume =_........ ³

A force called upthrust acts vertically upwards on the bubble.

When the bubble is released, it accelerates vertically upwards.

Draw two labelled arrows on the diagram to show the forces on the bubble as it is released.

The diagram shows a child’s toy for accelerating steel balls.

This is how the toy works.

• the toy uses three identical steel balls, each with a mass of 4.1 g

• ball A moves towards the magnet

• ball B is in contact with the magnet

• balls B and C are initially at rest and are in contact with each other

• when ball A collides with the magnet, ball C moves away from the magnet

Ball A moves towards the magnet with an initial velocity of 0.15 m/s.

Calculate the initial momentum of ball A.

initial momentum =_........ kg m/s

Ball A is attracted to the magnet.

Explain how this attraction affects the momentum of ball A as it approaches the magnet.

When ball A collides with the magnet, a force of 1.3 N is exerted on ball C for a time of 0.0025 s.

This causes ball C to move away from the magnet.

Calculate the change in velocity of ball C due to this force.

A ship floats on the sea.

The ship floats because of the forces acting on it.

The upward force acting on the ship is called upthrust.

This force is shown on the diagram.

Draw another labelled arrow on the diagram to show the other vertical force acting on the ship.

Forces are vector quantities.

State what is meant by the term vector quantity.

Give another example of a vector quantity.

The upthrust force acting on the ship is proportional to the pressure difference between the bottom of the ship and the surface of the sea.

The pressure acting on the ship at the surface of the sea is 100 kPa.

State the formula linking pressure difference, height, density and gravitational field strength (g).

The bottom of the ship is 15.8 m below the surface of the sea.

Show that the pressure acting on the bottom of the ship is approximately 260 kPa.

[density of seawater = 1030 kg/m³]

Explain why the bottom of the ship is deeper below the surface of the sea when the ship is fully loaded with cargo.

Diagram 1 shows a van accelerating along a horizontal road.

The horizontal forces acting on the van are shown.

Force X opposes the motion of the van.

State the name of force X.

The resultant force acting on the van is 1500 N.

Calculate the magnitude of force X.

[assume X is the only horizontal force opposing the motion of the van]

Diagram 2 shows the resultant force acting on the van when it brakes.

State the formula linking resultant force, mass and acceleration.

The mass of the van is 1900 kg.

Calculate the acceleration of the van when it brakes.

Give the unit.

The van was travelling at an initial speed of 18 m/s before braking and coming to rest.

Calculate the distance travelled by the van while it is braking.

[assume that the acceleration remains constant]

Describe two factors that would increase the braking distance.

When the van is fully loaded its mass increases to 2500 kg.

Calculate the time taken to bring the fully loaded van to rest when it is travelling at an initial speed of 18 m/s.

[assume that the resultant force during braking remains at 14 kN]