Friction

http://twyfordigcsephysics.blogspot.co.uk/2013/01/friction.html

Newton's 3rd law

http://twyfordigcsephysics.blogspot.co.uk/2012/12/newton-3.html

Assessed Homework

1.       (a)     (i)                                                                                                                  1 (L3)

(ii)                                                                  1 (L3)

the first mark is for an arrow pointing to the right,
with or without the label A
the arrow may be separate from, but parallel to, the rope

accept an arrow placed on the second drawing provided it is labelled A

the second mark is for an arrow pointing vertically downwards, with or without the label B

  (b)   any two from

·   air resistance or wind resistance  accept ‘wind’                                        2 (L4)

·   friction or water resistance

·   upthrust                                       accept ‘buoyancy’

·   lift                                               accept ‘drag’ as an alternative to wind

resistance or water resistance, but not both

accept ‘weight of the skis’

do not accept ‘weight’ or ‘gravity’ or water pressure’ or ‘resistance’

  (c)                                                                                                                         1 (L3)

the mark is for an arrow pointing to the left, with or without the label C the arrow may be separate from, but parallel to, the rope

accept an arrow placed on the first drawing provided it is labelled C

  (d)   any one from

·   it increases it                                accept ‘makes it accelerate’                  1 (L3)

·   it speeds it up

·   it makes it go faster

accept ‘faster’
do not accept ‘it changes it’

[6]

 

2.       (a)     Mars                                                 accept ‘6 kg’                                         1 (L5)
                                                         do not accept ‘24 N’

  (b)   any one from                                                                                                 1 (L5)

·   4 kg weighs more on Earth          accept the converse
                                                    ‘different weights’ is insufficient

·   the weight of the object is            accept the converse
greater on Earth                           accept ‘Earth is 40 N and Venus is 36 N’
                                                    accept ‘Earth is 40 and Venus is 36’
                                                    accept ‘more newtons on Earth’ or ‘less
                                                    newtons on Venus’

accept ‘there is a greater force on Earth’

do not accept ‘it has more mass on the Earth’

  (c)                                                            answers must be in the correct order

·   less (than) or smaller (than) or                                                                 1 (L6)
lower (than)

·   the same (as) or equal (to)                                                                        1 (L6)

  (d)   (i)      ·   the greater the distance       accept ‘it increases’                              1 (L5)
     the greater the time for
     one orbit

(ii)     ·   an answer from 1.6 to 6 inclusive                                                   1 (L6)

  (e)                                                                                                                         1 (L6)

award a mark for X marked on the orbit within the tolerances shown

[7]

 

  3.     (a)     B                                                                                                                   1 (L5)

(b)     (i)      A and C                                  accept ‘lift and weight’                         1 (L5)

answers may be in either order
both letters are required for the mark

  (ii)   D and B                                  accept A and C                                     1 (L5)

answers may be in either order
both letters are required for the mark

  (c)    (i)      ·   Force D is greater than                                                                     1 (L6)
     force B.                          if more than one box is ticked, award no mark

(ii)     ·   Force A is greater than                                                                     1 (L6)
     force C.                          if more than one box is ticked, award no mark

[5]

 

4.       (a)     150                                                                                                                        1

(b)     there is nothing to balance the force of the string                                                  1

accept ‘it is pushed by the string’ accept ‘there is a forward force acting on it’ accept ‘potential energy is converted to kinetic energy’ or ‘energy from the bow is transferred to the arrow’

  (c)   any one from                                                                                                        1

·   because they are not in opposite directions

accept ‘because they are in different directions’ or ‘because they are at an angle to each other’ or ‘because they are not both horizontal’
do not accept ‘because they are at an angle’

·   because they do not act along the same line

accept ‘gravity pulls down and friction pushes across’

  (d)   any one from                                                                                                        1

·   because the force is concentrated in a much smaller area

accept ‘because the area in contact is smaller’
or ‘because there is a smaller area’

·   because pressure is force divided by area

[4]

 

  5.     (a)     The tension equals the weight.      if more than one box is ticked,              1 (L6)
                                                         award no mark

  (b)   tension is greater than weight           accept ‘tension is bigger’ or ‘weight is less’ 1 (L6)

or ‘the upward force is bigger’ or ‘the downward force is smaller’

  (c)   tension equals weight                       accept ‘they are the same’                    1 (L6)

(d)     tension is less than weight                                                                             1 (L6)

accept ‘tension is less ‘or ‘weight is more’
or ‘the upward force is less’ or ‘the downward force is bigger’

[4]

 

6.       (a)     A                                                                                                                   1 (L5)

(b)     any one from                                                                                                 1 (L6)

·    he will remain stationary    accept ‘he floats’

·    he will continue moving at a constant speed

accept ‘nothing’

          any one from                                                                                                 1 (L6)

·    there is no net force

·    the pairs of forces are equal

accept ‘all the forces cancel out’

accept ‘they cancel each other out’

accept ‘the forces are balanced’

‘the forces are equal’ is insufficient

  (c)                                                       accept any arrow drawn going up and 1 (L6)
                                                         to the right

[4]

 

  7.     (a)     (i)      12.5 m/s                                  accept ‘ m/s’                                  1 (L7)
                                               accept ‘metres per second’ or ‘ms–1’ for m/s

the unit is required for the mark

do not accept ‘mps’

(ii)     they are equal or the same      accept ‘they are balanced’                   1 (L7)

  (b)   the forward force is greater than      accept the converse                              1 (L7)
the backward force                          accept ‘the forward force is greater’ or ‘the
                                                         backward force is smaller’

do not accept ‘the forward force becomes greater or increases’

          any one from                                                                                                 1 (L7)
·  because air resistance or drag is   accept ‘less friction’
   smaller or reduced
·  because there is a smaller surface
   area

‘she is more streamlined’ is insufficient as it is given in the question

[4]

 

  8.     (a)     (i)      constant speed or steady speed   accept not accelerating                    1 (L7)

(ii)     stationary or not moving             accept ‘steady speed of zero’           1 (L7)
or stopped

do not accept ‘it has a steady speed’

(b)     1.8                                                                                                1 (L7)
m/s                                                   accept ‘metres per second’ or ‘ms–1’    1 (L7)

do not accept ‘mps’

  (c)    (i)      The forward force was zero and friction was greater than zero.       1 (L7)

if more than one box is ticked, award no mark

  (ii)   6                                             accept answers from 5.8 to 6.2             1 (L7)

[6]

 

 

 

 

Newton's laws

http://twyfordigcsephysics.blogspot.co.uk/2012/11/blog-post.html