Page 8 - 20. Sci Phy Answer Key 2023 (AK016)
P. 8

(ii)  F =  ma =  52                                Let t = time taken to stop completely
                                      ´= 10 N
                             F =  F -  F                                          v - u   v (m/s)
                                 a   f                                         a =
                               =10  - 20  F                                         t
                                     f                                                   22.2
                                                                                       .
                             F = 10 N                                      -  .  =185  0 -222
                              f
                                                                                     t
                    (b) When a force of 10 N is applied from 30 s to           t = 12 s
                        40 s, the object moves with a constant speed                       0         t  t (s)
                        of 60 m/s because the resultant force acting on    (a is negative as it
                        the object is zero. When no force is applied on    is slowing down.)
                        the object from 40 s to 50 s, the speed of the     From the graph:
                        object  becomes  zero  because  frictional  force   Distance
                        slows down its motion.
                                                                           = (  1  )12  (  )22 2 .
                 4.  (a) F  − F  = 0 N                                       2
                         a   f                                             = 133  m
                        F  = F
                         a   f
                        Frictional force = 8 N.
                    (b) mass of carton = 2.5 kg                6.  (a) F = (2.5)(0.5) = 1.25 N
                        F = 2.5 × 1.25 = 3.125 N                   (b) Frictional force = 8 − 1.25 = 6.75 N
                        F = F  − F                                 (c) v = u + at = 0 + (0.5)(4) = 2 m/s
                            a   f
                        3.125 = F  − 2.4                           (d) (i)    -675
                                                                                 .
                                a
                        F  =3.125 + 2.4 = 5.525 N ≈ 5.53 N                 a =      =-27 . m/s 2
                         a                                                     25 .
                    (c)  F =  F -  a  F =  f  - 6500  4000  = 2500  N      Deceleration = 2.7 m/s 2
                           F   2500
                        a =  =      = 625  m/s 2                           [The frictional force will be the only force
                                      .
                           m    400                                        acting on the box to slow it down. The
                    (d)  F =  F -  a  F =  f  - 4500 1500  = 3000  N       negative sign indicates the force acts in
                            F  3000                                        the opposite direction to the motion of
                        m =  =      = 600  kg                              the box.]
                            a    5                                    (ii)  Let t = time taken v (m/s)
                    (e)  F =  ma =  40.  = 75  3  N                        to stop completely.
                                 ´
                        F =  F -  a  F f                                      a =  v - u  2
                          = 3  F -  a  1  5                                        t
                        F = 18 N                                           -   =27 .  0 -2
                         a
                                                                                   t      0         t  t (s)
                                                                              t = 0 7407.  s
                 5.  (a) (i)            80000
                             v =      = 80 km/h  = 22 2 .  m/s             (a is negative as it is slowing down.)
                                         3600
                                22 2 .  -0                                         1
                             a =       = 222 m/s 2                         Distance = ()(  20.  ) 7407
                                         .
                                  10                                                2
                                        =
                                     .
                             F =   ´ 800 222 = 1776 N                             = 0 741  m
                                                                                    .
                        (ii)  0 N
                    (b)    0 -222 .                            Revision 2
                        a =       =-444 m/s 2
                                      .
                              5                                1.  (a)
                        F =   ´ 800  -  .  =444  -3552 N
                        The braking force is 3552 N. (in opp direction)
                    (c) (i)       1776
                               a =     =  185 m/s 2
                                          .
                                   960
                                  u
                               v =+  at
                                      185)
                             22.  = 2  + 0  ( .  t                                       [The  normal  force
                               t = 12 s                                                  must   always   be
                        (ii)            1                                                perpendicular   to
                             Braking force =  ´  -  =3552  -1776  N                      the  surface  of  the
                                        2                                                plane/ground.   The
                                -1776                                                    weight  must  always
                                          .
                             a =      =-185  m/s 2                                                            Answer Key
                                 960                                                     be in the direction of
                            (a is negative as it is slowing down.)                       vertical downward.]
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