Parachutes

http://twyfordigcsephysics.blogspot.co.uk/2013/01/parachutes-and-freefall.html

Assessed Homework

1.       (a)     points plotted correctly;;         [Deduct 1 mark for each error]                         2
[Line not necessary]

  (b)   3 (m/s);                                                                                                             1

  (c)    (i)      acceleration = change in velocity / time taken;                                                              1
[Accept a =  (v-u)/t

  (ii)   acceleration = 3/15 ; [Allow ecf from part (b)]
                   = 0.2 (m/s2);                                                                         2

[6]

 

  2.     C

[1]

 

  3.     (i)      acceleration (due to gravity) / gravitational field strength                                 1

  (ii)   m / s2 or N / kg                                                                                                 1

[2]

 

  4.     (a)     A description to include:

          1. upward push/reaction/thrust;
2. of the ground on the athlete;                                                               2

  (b)   (i)      A calculation to include:

          1. acceleration = (v-u)/t
2. substitution of correct data,
3. = 9.7 m/s2; [Accept –9.7 m/s2]                                                   3

(ii)     downwards;
negative gradient/backwards slope/athlete slowing down/retardation/
deceleration;                                                                                            2

(iii)    A calculation to include:

          1. F        = ma;
2.           = 65 kg ´ 9.7 (m/s2);[Allow ecf from b(iii)]
3.           = 630 – 633 (N);
[Accept either 65 ´ 10 m/s2 = 650 N for 2 marks
or        65 ´ 9.81 m/s2 = 638 N for 2 marks]                                  3

(iv)    downward pull of the Earth/gravitational pull;
[Reject gravity]                                                                                        1

[11]

 

  5.     (a)     15 (m/s)                                                                                                            1

(b)     acceleration = change in speed ÷ time;
                   = 15 m/s ÷ 1.5 s;
                   = 10 m/s2;                                                                                      3

  (c)    (i)      the acceleration decreases

(ii)     this is shown by the decreasing slope/ gradient of the graph                   2

  (d)   at Pisa, air resistance affected the objects ;
the lighter object was affected more than the heavy one
there is no air on the Moon, so both objects had the same
acceleration/ neither object was affected by air resistance                                3

[9]

 

  6.     (a)     resultant/net/unbalanced force is in forwards direction
/950>550 /driving force>resistive force/
forwards force is greater than backwards force;                                               1

  (b)   Ignore      F = ma (or in words)
acceleration   = force/mass;
                     = 400 (N) / 850 (kg);
                     = 0.47 (m/s2);                                                                              3
Bald 0.5 gains no marks
If acceleration = 1.12 (m/s2) award TWO marks maximum only

  (c)   the driving force becomes zero; Accept decreases OWTTE;
the overall resistive force increases/braking force is added/air
resistance decreases;
plus 1 communication mark for ensuring that spelling,
punctuation and grammar are accurate, so that the meaning is clear;                3

[7]