• 9702 June 2011 Paper 22 Worked Solutions | A-Level Physics

Paper 22

Question 1

(a)

Distinguish between scalar and vector quantities:

A scalar quantity has only a magnitude while a vector quantity bas both a magnitude and a direction.

(b)

Underline all scalars:

Acceleration    force    kinetic energy              mass    power  weight

(c)

Stone thrown with horizontal velocity of 20ms-1 from top of cliff 15m high. Path of stone shown. Air resistance negligible.

For the stone,

(i)

Time to fall 15m:

s = ut + ½at²

15 = 0 + ½(9.81)t²    

t = 1.7s

(ii)

Magnitude of resultant velocity after 15m:

Let the vertical component be v_v

v_v² = u² +2as = 0 + 2(9.81)(15)           or  v_v = u +at = 0 + 9.81x1.7(5)

v_v = 17.16ms^-1

So, for resultant velocity: v² = (17.16)² + (20)²

v = 26ms^-1  

(iii)

Difference between displacement of stone and distance that it travels:

The distance is the actual path travelled. The displacement is the straight line distance between start and finish points (in that direction) / minimum distance.

Question 2

{Detailed explanations for this question is available as Solution 491 at Physics 9702 Doubts | Help Page 95 - http://physics-ref.blogspot.com/2015/03/physics-9702-doubts-help-page-95.html}

Question 3

(a)

(i)

Work done is equal to the product of force and the distance moved / displacement in the direction of the force.

(ii)

Power is defined as the rate of doing work / work done per unit time.

(b)

Fig shows part of fairground rode with a carriage on rails. Carriage and passengers have total mass of 600kg. Carriage travelling at speed of 9.5ms^-1 towards slope inclined at 30^o to horizontal. Carriage comes to rest after travelling up slope to a vertical height of 4.1m.

(i)

Kinetic energy in kJ of carriage and passengers as they travel towards slope:

KE = ½mv² = 0.5 x 600 x (9.5)² = 27075J = 27kJ

(ii)

Show gain in potential energy of carriage and passengers = 24kJ:

PE = mgh = 600 x 9.81 x 4.1 = 24132J = 24kJ

(iii)

Work done against resistive force as carriage moves up slope:

Work done against resistive force = 27 – 24 = 3.0kJ

(iv)

Use answer to (iii) to calculate resistive force acting against carriage as it moves up slope:

the distance along slope = 4.1 / sin30^o = 8.2m

Resistive force = 3000 / 8.2 = 366N

Question 4

Student measures Young modulus of a metal in the form of a wire.

(a)

Describe, with aid of diagram, the apparatus that could be used:

A clamped horizontal wire a pulley or a vertical wire attached to ceiling with mass attached.

Details: a reference mark on wire with a fixed scale alongside

(b)

Method used to obtain required measurements:

The original length of the wire is measured up to the reference mark with a metre ruler / tape. The diameter of the wire is measured with a micrometer / digital calipers. The initial and final reading (for the extension) of the wire is measured with a metre ruler or other suitable scale. The mass or weight used for the extension is measured / recorded.

Some good physics method:

The diameter is measured in several places / remove the load and check whether the wire returns to its original length / take several readings with different loads  

(c)

How measurements taken can be used to determine Young modulus:

The extension is determined from the final and initial readings. A graph of force against extension is plotted and the gradient of the graph for F/e is determined. The area is calculated from πd²/4.

The Young modulus, E is calculated from E = Fl / eA or (gradient x l/A)

Question 5

{Detailed explanations for this question is available as Solution 522 at Physics 9702 Doubts | Help Page 101 - http://physics-ref.blogspot.com/2015/04/physics-9702-doubts-help-page-101.html}

Question 6

{Detailed explanations for this question is available as Solution 636 at Physics 9702 Doubts | Help Page 126 - http://physics-ref.blogspot.com/2015/04/physics-9702-doubts-help-page-126.html}