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

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(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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