NCEA Level 2 Physics (90255) 2010 — page 1 of 4
Assessment Schedule – 2010
Physics: Demonstrate understanding of mechanics (90255)
Evidence Statement
Q
ONE
(a)
Evidence
Achievement
Merit
1
v
Both correct.
Must have labels, arrows
and must be at right
angles to each other.
a
(b)
1
Correct direction for
arrow.
1
There is no
unbalanced force,
so it travels in a
straight line.
OR
No acceleration
and hence travels
in a straight line.
2
Correct working except
for one error.
If candidate has
substituted correctly for
2
Correct working
and answer.
1
Description all
correct.
2
Correct vertical
component
OR
used v =23.52 to
calculate v
(v = 39.5 m s–1)
There is no horizontal unbalanced force
on the discus. Since there is no
unbalanced force, there is no acceleration,
and hence it travels in a straight line.
(c)
TWO
(a)
(b)
Excellence
mv 2
F=
r
2.1 ! 112
290 =
r
2.1 ! 112
r=
290
r = 0.88 m
290 =
Correct except for one
error.
Downwards 9.8 m s–2
1
Both correct.
Must have size AND
direction. Accept 10 m
s–2.
2
Calculates speed using t
= 2.4 s.
v = 23.52ms-1
OR
Used an incorrect value
for time.
(c)
vh
Consider vertical motion
vf = vi + at
2.4
2
vi = 11.76
11.76
v
v = 19.5 m s!1
sin 37° =
2
Correct working and
answer.
OR
If candidate has
transposed incorrectly
290
and got r =
2.1 ! 121
1
0 = vi ! 9.8 "
There is no
acceleration, due to
the absence of an
unbalanced force,
and hence it travels
in a straight line.
2.1 ! 112
r
As it rises, kinetic energy changes to
gravitational potential energy.
As it falls, gravitational potential energy
is converted to kinetic energy.
As it rolls, kinetic energy is converted to
heat.
v
1
NCEA Level 2 Physics (90255) 2010 — page 2 of 4
(d)
THREE
(a)
1
Greater range.
2
Correct answer.
Two significant figures because this is the
smallest number of significant figures in
the data.
1
Correct answer.
When she lands an upward force causes
her to stop.
Her momentum change is !p = F !t
The size of her momentum change is
unaffected
so the padded mat causes her to stop in a
longer time.
This means there is a smaller force acting
on her.
OR
Work must be done to stop her.
W = F!d
The size of the work done is unaffected,
so the padded mat causes her to stop in a
longer distance.
This means there is a smaller force acting
on her.
OR
Explains in terms of acceleration:
Since change in velocity is over a longer
period of time, so less acceleration since
!v
. Since F = ma, a smaller
a=
t
acceleration would mean a smaller force
when landing on the padded mat.
1
2
• If there is a lift force, the total force
downwards is smaller.
• So the downward acceleration is
smaller.
• So the discus is in the air for a longer
time.
• So the range is greater.
OR
The lift force allows discus to fly higher
and hence it is in the air for longer.
Since horizontal velocity is constant,
then a greater distance is travelled in
greater time. Hence range is greater.
d = vi t +
1 2
at
2
1
Greater range
because the discus
is in the air for a
longer time.
1
Full explanation.
(accept either reason
1 OR reason 2)
OR
a combination of 1
and 2 so long as they
have 4 bullet points.
Decreases the size of the
force acting on her body.
OR
Longer time and hence
smaller impact
OR
Transfers energy over a
longer period of time.
1
Decreases the size
of the force acting
on her body
because stopping
time increases.
OR
Decreases the size
of the force acting
on her body
because stopping
distance increases.
1
Full explanation.
Correct acceleration.
OR
Correct Δp
2
Correct answer.
1
! 2.21 ! 2.02
2
d = 4.42 m = 4.4 m
d = 0+
(b)
(c)
FOUR
(a)
!v 11 " 0
=
= 44 m s"2
!t
0.25
F = ma = 5.4 # 44 = 240 N
a=
OR
F !t = m!v
F # 0.25 = 5.4(11 " 0)
F = 240 N
NCEA Level 2 Physics (90255) 2010 — page 3 of 4
(b)
Because friction is negligible there are no
net outside forces so the total momentum
remains constant.
1
Total momentum
constant.
OR
Momentum of stationary
shot increases.
1
Achievement plus
one explanation.
1
Full explanation
(last sentence is not
essential but can
provide evidence).
*Must have TWO
statements and a
reason for each
statement – one for
total momentum and
one for momentum
of 4 kg shot.
2
Correct equation and
substitution.
OR
Gets 8.1 and
9.6 kg ms–1 correct.
2
Correct answer to
final speed.
2
Correct answer to
final velocity
including size and
direction.
2
Correct except for unit
conversion OR weight
calculation.
2
Correct calculation
and answer.
*Ignore negative
sign
The momentum of the stationary shot
increases because there is an outside
(unbalanced) force on it.
Momentum gained by stationary shot =
momentum lost by thrown shot.
OR The 5.4 kg shot transfers some of its
momentum to the 4 kg shot.
(c)
!p =!p
i
f
5.4 " 1.5 # = 5.4v + 4.0 " 2.4 #
8.1 # $9.6 # = 5.4v
v = 0.28 m s $1
FIVE
(a)
(b)
%
F = kx
F
k=
x
539
k=
= 1.8 ! 105 N m "1
0.003
E = 12 kx 2
*If used mass = 55 kg and
x = 3 then NA (two
errors).
1
Correct unit.
2
Correct answer.
1
One correct statement.
1
Both statements
correct.
2
Correct equation and
substitution (line 2).
Even though g cancels
out, it must be included
in the equation unless it
is clearly stated that it
cancels.
2
Correct answer for 2 Correct answer.
W =121 N
Accept either
OR
12.3 kg or 1
If used
0.6 kg
g = 10 m s–2, then
W = 106.6 N
OR
Got one error in
substitution but
got rest of method
correct.
E = 12 ! 1.8 ! 105 ! 0.0032
E = 0.81 J
OR
Solves using E = 12 Fx
(c)
The total force is zero and the total torque
is zero.
(d)
! C = ! AC
W " 1.5 + (539 " 2) = 420 " 3
1260 # 1078
= 121 N
1.5
W 121
m=
=
= 12.3 kg = 12 kg
g 9.8
OR
m = 10.6 kg (if used with g = 10 N kg–1)
W=
NCEA Level 2 Physics (90255) 2010 — page 4 of 4
Judgement Statement
Achievement
Achievement with Merit
Achievement with Excellence
10 correct answers including
3 A1 + 2 A2
11 correct answers with 8 M
including 2 M1 + 2 M2
12 correct answers with 5 M + 4 E
including 1 E1 + 1 E2