Effects of Forces (Cambridge (CIE) IGCSE Physics): Exam Questions

A student stretches a spring by adding different loads to it. She measures the length of the spring for each load. She plots a graph of the results.

Fig. 2.1 shows the graph of her results.

Use the graph to determine:

(i) the length of the spring without a load

length = .................................................. cm [1]

(ii) the length of the spring with a load of 4.0 N

length = .................................................. cm [1]

(iii) the extension due to a 4.0 N load.

extension = .................................................. cm [1]

Complete the sentence about effects of forces. Choose words from the box.

Stretching a spring with a load is an example of how a force can change the .................................... and the .................................... of an object.

Fig. 3.1 shows the vertical forces on a rocket.

Calculate the resultant force on the rocket.

resultant force = ........................................................... N

direction = ...........................................................

Fig. 3.2 shows the speed and direction of motion of an object at a point in time.

The resultant force on the object is zero for 10 seconds.

Deduce the speed and direction of motion after 5 seconds. Indicate the speed and direction of the object by drawing a labelled arrow next to the object in Fig. 3.3.

Fig. 3.1 shows a spring with no load attached. Fig. 3.2 shows the same spring with a load attached.

Describe how a student can determine the extension of the spring. You may draw on Fig. 3.1 and Fig. 3.2 as part of your answer.

The student plots a graph of load against extension, as shown in Fig. 3.3.

(i) Determine the extension produced by a load of 7.5 N.

extension = ...................................................... cm [1]

(ii) Determine the load that would produce an extension of 10.0 cm. 

load = ...................................................... N [1]

Calculate the mass that has a weight of 6.0 N.

mass = ...................................................... kg 

Fig. 3.1 shows the horizontal forces acting on a swimmer.

(i) Calculate the size and direction of the resultant horizontal force on the swimmer.  

size of resultant horizontal force = ...................................................... N

direction of resultant horizontal force = ......................................................    

[1]

(ii) State the name of the 110 N force on the swimmer.

[1]

(iii) Fig. 3.2 shows the horizontal forces acting on the swimmer as he moves forwards a short time later.

Describe and explain the motion of the swimmer.

[2]

Another swimmer weighs 700N. He stands on a diving board, as shown in Fig. 3.3.

Calculate the moment of the swimmer’s weight about point P.

moment = ...................................................... N m 

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A car travels around a circular track at constant speed.

Explain why it is incorrect to describe the circular motion as having constant velocity.

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A force is required for the car to maintain the circular motion.

Explain why a force is required.

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State the direction in which the force acts for objects in circular motion.

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State the name of this force for the car on the track.

 Fig. 1.1 is the distance–time graph for the car from t = 0.

(i) State the property of a distance–time graph that corresponds to speed. 

[1] 

(ii) Using Fig. 1.1, determine the initial speed v of the car. 

v = ......................................................... [2]

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When the car is decelerating, there is a constant resistive force F on the car due to the brakes. 

The deceleration of the car is greater than and is not constant. 

Explain why: 

(i) the deceleration of the car is greater than

 [1] 

(ii) the deceleration is not constant.

[2] 

A student investigates the stretching of a spring. The apparatus is shown in Fig. 1.1.

Fig. 1.1

The student measures the length of the unstretched spring. Fig. 1.2 shows the spring next to the metre rule.

Fig. 1.2

(i) By taking scale readings from the metre rule in Fig. 1.2, calculate the unstretched length of the spring in cm.

[2]

(ii) State one precaution the student should take to obtain an accurate length reading.

[1]

The student hangs various loads on the spring and measures the new length each time. The results are shown in Table 1.1.

Table 1.1

Calculate, and record in Table 1.1, the extension of the spring for each load . Use the equation .

Plot a graph of / cm (y-axis) against / N (x-axis). Start the axes at the origin (0,0).

Draw a best-fit straight line.

(i) Determine the gradient of your line. Show clearly on the graph how you obtained the value.

[1]

(ii) Calculate a value for the spring constant of the spring using the equation

Include the unit.

[2]

A student is using some 50 g masses.

Calculate the weight of one 50 g mass.

weight of 50 g mass = ...................................................... N 

The student uses the 50g masses as loads to stretch a spring.

Fig. 2.1 shows the apparatus the student uses to obtain readings for a load-extension graph.

Describe how the student could use the apparatus and ensure that the readings are accurate.

The mass of a small steel ball is 120 g. The volume of the ball is 16.0 cm³.

(i) Calculate the density of the steel ball.

density = ............................................... g / cm³ [3]

(ii) The ball falls to the ground from rest. At a time of 0.2 s after it started to fall, its acceleration is 10 m / s².

State the acceleration of the ball at a time of 0.1 s after it started to fall.

[1]

Fig. 3.1 shows the vertical forces that act on a large plastic ball as it is falling.

(i) State the name given to each of the forces shown in Fig. 3.1.

[1]

(ii) Calculate the size of the resultant force on the ball.

resultant force = ...................................................... N [1]

A load is attached to a spring, as shown in Fig. 3.1. Two arrows indicate the vertical forces acting on the load. The spring and the load are stationary.

(i) State the name of the force acting vertically downwards.

[1]

(ii) The vertical force that acts upwards is 4.0 N.  

State the value of the force acting vertically downwards.

force = ..................................................... N [1]

The load is pulled downwards and then released. The load moves up and down.

Fig. 3.2 represents the vertical forces acting on the load at some time after it is released.

Calculate the resultant force on the load and state its direction.

resultant force = ........................................................... N

direction = ............................................................... 

(i) State the principle of conservation of energy.

[1]

(ii) Eventually the load stops moving up and down.

Describe and explain why the load stops moving. Use your ideas about conservation of energy.

[2]

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Fig. 1.1 shows an aeroplane accelerating uniformly on a runway. 

Fig. 1.1

The aeroplane has a mass of 3.1 × 10⁶ kg. 

From rest, the aeroplane reaches a speed of 70 m/s after 32 s.

Calculate the following quantities

(i) The acceleration of the aeroplane.

acceleration = .................................... [2]

(ii) The resultant force acting on the aeroplane.

resultant force = .................................... [2]

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When the aeroplane reaches its destination, air traffic control directs it to circle the airfield until there is a safe time to land.

Fig. 1.2 shows a head on view of the aeroplane flying at a constant speed in a circular horizontal path. 

Fig 1.2

Draw an arrow showing the resultant force on the aeroplane.

Explain your answer.

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The pilot wants to decrease the radius of the circular flight path whilst maintaining a constant speed.

Suggest how the pilot could achieve this.

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As the aeroplane lands on the runway, it decelerates from its top speed. The resultant force on the aeroplane is less than it was at take off. 

Explain why this is the case.

A resultant force acts on an object at rest. 

State the direction of the acceleration.

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A resultant force acts perpendicularly on a object traveling at a constant speed. 

State the effect of the force on the object.

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A man with a mass of 70 kg steps into an elevator. 

(i) State the value of the force exerted on the man by the elevator. 

force = .................................... [1]

(ii) Calculate the force required to accelerate the man at 1.6 m/s².

force = .................................... [1]

(iii) Explain why these values are different.

[2]

A cyclist starts from rest and accelerates along a straight, level road. The cyclist then travels at a constant speed before decelerating to a stop.

Fig. 1.1 shows the speed–time graph for the cyclist's journey.

Fig. 1.1

Define acceleration.

Explain, in terms of forces, why the cyclist travels at a constant speed between 8.0 s and 28 s.

Calculate the total distance travelled by the cyclist.

Show your working.

On a different day, the cyclist makes the same journey, but there is a strong headwind. The cyclist pedals with the same driving force as before.

Explain why this leads to a longer journey time.