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O LevelPhysicsCambridgeExam Questions1. Motion, Forces & Energy1.5 Forces

Forces (Cambridge O Level Physics)

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1.5 Forces

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1.5 Forces

1a2 marks

The class is investigating the behaviour of a spring, and then using the spring to determine the weight of an object.

The apparatus is shown in Fig. 3.1.

p1-3a

The stretched length l of the spring, indicated in Fig. 3.1, is to be measured.

 
Describe two precautions that could be taken when measuring the length of the stationary spring, to ensure an accurate reading. You may draw a diagram.

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1b1 mark

A student measures the length l subscript 0 of the spring without any load.

l subscript 0 = 2.1 cm

Various loads L are hung on the spring.
The stretched length l of the spring for each load is recorded in Table 3.1.

 

Table 3.1

L/N l/cm e/cm
1.0 6.3  
2.0 10.5  
3.0 14.7  

 

Calculate, and record in Table 3.1, the extension e of the spring for each load L.
Use the equation e space equals space open parentheses l minus l subscript 0 close parentheses

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1c1 mark

The loads are removed and an object X is suspended from the spring.

 

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The unstretched length l subscript x of the spring on Fig 3.2 is 11.4 cm

Estimate the weight WX of object X.

Explain how you obtained your answer.

 
 WX = ........................................................... N 

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1d1 mark

A student measures the weight of a different load using a similar method. He gives the weight as 4.532 N.

Explain why this is not a suitable number of significant figures for this experiment.

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1e4 marks
(i)
Another student suggests that e is directly proportional to L.
 
State whether the results support her suggestion.
 
Use values from the results in Table 3.1 to justify your statement.
[2]
 
(ii)

The student wishes to plot a graph of L against e to test if the two quantities are directly proportional.

 

State how her graph line could show that e is directly proportional to L.

[2]

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2a1 mark
A student is determining the spring constant k of a spring by two methods.
   
Fig. 1.2 shows how the apparatus is used.
   
Method 1
   

On Fig. 1.1, measure the unstretched length l subscript 0 of the spring, in mm.

screenshot-2022-11-08-at-09-54-01
l subscript 0 = ................................................. mm 

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2b2 marks

Extended tier only

The student attaches the spring to the clamp as shown in Fig. 1.2.

He hangs a 300 g mass on the spring.

screenshot-2022-11-08-at-09-57-59

He measures the new length l of the spring.

   
l = 53 mm
   
(i)
Calculate the extension e of the spring using the equation e space equals space l space minus space l subscript 0.
   
   
e = ................................................. mm [1]
   
(ii)
Calculate a value for the spring constant k using the following equation:
 k space equals space F over e ,
where F = 3.0 N.
   
   
k = ............................................ N/mm [1]

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2c4 marks
Method 2
   

The student pulls the mass down a short distance and releases it so that it oscillates up and down. Fig. 1.3 shows the time t taken for 10 complete oscillations.

screenshot-2022-11-08-at-10-10-55
(i)
Record the time t taken for 10 complete oscillations.
   
   
t = ........................................................ [1]
 
(ii)
1.   Calculate the time T taken for one complete oscillation.
   
   
T = .............................................................
   
2.   Calculate T 2.
   
   
T 2 = .............................................................
[2]
   
(iii)
Calculate the spring constant k using the following equation:
k space equals space fraction numerator 0.040 m over denominator T to the power of space 2 end exponent end fraction,
where m = 0.300kg.
   
   
k = ............................................ N/mm [1]

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2d2 marks

State and explain whether your two values for k are the same within the limits of experimental accuracy.

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2e2 marks

A student states that repeating Method 1 with different masses would improve the reliability of the value obtained for k.

Suggest additional values for the mass m that you would use when repeating the experiment to improve the reliability.

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37 marks

A student wants to investigate the effect of air resistance on the swing of a pendulum.

Plan an experiment which will enable him to investigate how air resistance changes the way in which a pendulum swings.

The apparatus available includes:

a light wooden rod, approximately 80cm long with a hole at one end, through which a nail will fit

a piece of modelling clay to act as a pendulum bob, as shown in Fig. 4.1

a sheet of thick card which will provide the air resistance when the pendulum swings.

In your plan, you should:

  • list any additional apparatus needed
  • explain briefly how you would carry out the experiment including exactly which measurements should be taken
  • state the key variables that you would control
  • draw a table, or tables, with column headings, to show how you would display your readings (you are not required to enter any readings in the table)
  • explain how you would use your readings to reach a conclusion.

You may add to Fig. 4.1 or draw an additional diagram if it helps to explain your plan.

p4-4

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