Resultant forces

In a dog-sled race, a team of dogs pull on a rope attached to a sled.

Figure 12 shows a dog-sled team.

Use the Physics Equations Sheet to answer questions 06.1 and 06.2.

What equation links distance travelled, speed and time?

Tick () one box.

The longest dog-sled race in the world covers a distance of 1 500 000 m.

One team finished the race in a time of 670 000 s.

Calculate the average speed of this team during the race.

At the start of the race, 6 dogs pulled on the rope.

The average forward force on the sled from each dog was 370 N.

The backwards force on the sled from friction was 520 N.

Calculate the resultant force on the sled.

Figure 13 shows a distance–time graph for the sled at the start of the race.

What does the gradient of the graph in Figure 13 represent?

Later in the race, the sled moved at a constant speed along a flat, horizontal path.

What was the relationship between the size of the horizontal forces acting when the sled moved at a constant speed?

Tick () one box.

The rope exerted a force on the sled when the sled was moving.

What is the Newton’s Third Law pair to the force of the rope on the sled?

Tick () one box.

In a dog-sled race, a team of dogs pull on a rope attached to a sled.

Figure 1 shows a dog-sled team.

Use the Physics Equations Sheet to answer questions 01.1 and 01.2.

What equation links distance travelled, speed and time?

Tick () one box.

The longest dog-sled race in the world covers a distance of 1 500 000 m.

One team finished the race in a time of 670 000 s.

Calculate the average speed of this team during the race.

At the start of the race, 6 dogs pulled on the rope.

The average forward force on the sled from each dog was 370 N.

The backwards force on the sled from friction was 520 N.

Calculate the resultant force on the sled.

Figure 2 shows a distance–time graph for the sled at the start of the race.

What does the gradient of the graph in Figure 2 represent?

Later in the race, the sled moved at a constant speed along a flat, horizontal path.

What was the relationship between the size of the horizontal forces acting when the sled moved at a constant speed?

Tick () one box.

The rope exerted a force on the sled when the sled was moving.

What is the Newton’s Third Law pair to the force of the rope on the sled?

Tick () one box.

Figure 1 shows a skydiver jumping from an aeroplane.

The skydiver is accelerating downwards.

Which force causes the skydiver to accelerate?

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Which force increases as the skydiver accelerates?

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Figure 2 shows the two forces acting on the skydiver a few seconds after jumping from the aeroplane.

Calculate the resultant force acting on the skydiver in Figure 2.

Eventually the skydiver stops accelerating and falls at a constant velocity.

What is the resultant force acting on the skydiver when falling at a constant velocity?

Tick () one box.

What name is given to the constant velocity of the skydiver?

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Figure 3 shows a velocity–time graph for the skydiver.

How many seconds did the skydiver accelerate for?

Use Figure 3.

What was the constant velocity of the skydiver?

Use Figure 3.

After opening a parachute, the skydiver fell at a constant speed of 3.6 m/s for 25 seconds.

Calculate the distance travelled by the skydiver during this time.

Use the equation:

distance travelled = speed × time

Figure 11 shows a stationary apple hanging from a tree. The X marks the centre of mass of the apple.

Draw two arrows on Figure 11 to show the forces acting on the apple.

It takes 0.50 s for the apple to fall to the ground. The initial velocity of the apple is 0 m/s acceleration due to gravity = 9.8 m/s² Calculate the distance fallen by the apple. Use the Physics Equations Sheet.

In Question 07.2 it was assumed that the acceleration was a constant 9.8 m/s² Evaluate this assumption.

Forces are either contact forces or non-contact forces.

Which of the following is a non-contact force?

Tick (✓) one box.

Figure 1 shows a person standing on some bathroom scales.

The person exerts a downward force on the scales and the scales exert an upward force on the person.

Which sentence about the forces is true?

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What is the name of the upward force on the person?

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The person on the scales has a mass of 55 kg.

gravitational field strength = 9.8 N/kg

Calculate the weight of the person.

Use the equation:

weight = mass × gravitational field strength

The gravitational field strength is not the same at all points on the surface of the Earth.

The gravitational field strength is weakest at the equator.

A person travelled from the UK to the equator.

What happened to the weight of the person?

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Figure 2 shows the forces acting on a person.

The person is about to jump.

The arrow representing the weight of the person is drawn from point X.

What is the name given to point X ?

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Determine the size of the resultant force on the person in Figure 2.

Scientists are developing a rocket aeroplane designed to travel much faster than jet aeroplanes.

The rocket aeroplane must accelerate along a runway to take off.

What would happen to the air resistance acting on the rocket aeroplane as it accelerates?

During the first 14 seconds the average speed of the rocket aeroplane on the runway will be 35 m/s.

Calculate the distance that the rocket aeroplane will travel during the first 14 seconds.

Use the equation:

distance travelled = average speed × time

Write down the equation which links distance (s), force (F) and work done (W).

When the rocket aeroplane travels a distance of 270 m on the runway the engines will do 54 000 000 J of work.

Calculate the average force exerted by the engines.

The rocket aeroplane will fly at a greater height than a jet aeroplane.

The height that an aeroplane flies at affects the radiation dose a passenger will receive each hour.

Table 2 shows the speed of each aeroplane and the radiation dose a passenger will receive each hour.

Exposure to ionising radiation has risks and possible consequences.

Evaluate the risks and possible consequences of flying in a rocket aeroplane and in a jet aeroplane.

Assume the same journey is made in each aeroplane.

Use values from Table 2.

Figure 4 shows two children playing table tennis.

The boy hits the ball from one end of the table.

Why does the velocity of the ball change when the boy hits it?

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The ball has an average speed of 11 m/s

The ball takes 0.25 s to travel the same distance as the length of the table.

Calculate the length of the table.

Use the equation:

distance travelled = speed × time

A table tennis ball should only be used if it bounces to at least 75% of the height it was dropped from.

A manufacturer tested a table tennis ball.

Table 1 shows the results.

Determine whether the ball can be used.

Use the data from Table 1.

Figure 5 shows two table tennis balls.

The balls are different sizes but have the same mass.

Both balls were dropped onto the table from the same height.

After they were dropped, the resultant force on the smaller ball was greater than the resultant force on the larger ball.

Explain why.

Figure 9 shows a free body diagram for an aeroplane flying at a constant speed and at a constant height.

The speed of the aeroplane is much greater than the speed at which the aeroplane lands.

Explain how the forces need to change so the aeroplane can land.

The aeroplane lands at a speed of 80 m/s

After landing, the aeroplane takes 28 s to decelerate to a speed of 10 m/s

The mean resultant force on the aeroplane as it decelerates is 750 000 N

Calculate the mass of the aeroplane.

Figure 10 shows the horizontal forces acting on a man swimming in the sea.

Describe the movement of the man when the resultant horizontal force is 0 N

The man increases Force A. Explain what happens to Force B and to the movement of the man.

A boat moves through the sea. There is a 3000 N force to the west on the boat. There is a 1000 N force to the south on the boat. Determine the magnitude and direction of the resultant force on the boat. Draw a vector diagram of these forces to scale on Figure 11

The force to the south on the boat increases. What effect does this have on the resultant force on the boat?