P2 Topic 4: Momentum energy work and power
Friday, 13 March 2015
Additional Science Revision
Model Answers
Stopping
Thinking
Braking
Y
Y
Y
Bigger mass means more kinetic energy which takes longer to
transfer to heat using friction.
Speed = distance / time
Y
Might not see or hear something until later
Y
Affects the speed that our brain processes signals
Y
Converts kinetic energy to heat at a slower rate
Y
Reduces friction
Reduces friction
Y
P2 Topic 4: Momentum energy work and power
Friday, 13 March 2015
Additional Science Revision
Model Answers
Collect a range of different surfaces of similar size. Connect the block to a force-meter, place the
block on top of the first surface and a 500g mass on top of the block to ensure good contact
between the block and the surface. Pull the block across the surface and record the force
required to get it moving. Repeat until you get 4 concordant results then repeat for the other
surfaces.
direction
1200kg
5m/s
p=mxv
p= 1200 x 5
6000
kgm/s
size
It has size but no direction.
P2 Topic 4: Momentum energy work and power
Friday, 13 March 2015
Additional Science Revision
Model Answers
line
total
collision
12 000kg
1.5 m/s
p=mxv
p=12 000 x 1.5
18000
kgm/s
the same
27 000kg
18 000 kgm/s
p=mxv
v=p/m
v=18000/27000
0.67
m/s
P2 Topic 4: Momentum energy work and power
Friday, 13 March 2015
Additional Science Revision
Model Answers
high
zero
low
All of these active safety features work by increasing the collision time, this reduces
the collision force and reduces injuries to the driver and passengers.
An accelerometer is attached securely to the trolley, using sellotape. Bubble wrap is used to
create crumple zones of different thicknesses that are attached to the front of the trolley one
at a time. The car is rolled down a ramp of specific height, length and steepness and crashed
into a pile of textbooks that is kept the same for each test. The deceleration from the
accelerometer could be used to calculate the force on the trolley using F=mxa
P2 Topic 4: Momentum energy work and power
Friday, 13 March 2015
Additional Science Revision
Model Answers
12 000kg
0 m/s
5 m/s
0.1s
30m
150N
F=(v-u)/t
1 m/s
0.0005s
100N
E=150x30
4500
J
F=(0-5)/0.1
-50
N
30m
0.2 kg
E=Fxd
F=(v-u)/t
Ft=v-u
-(Ft+v)=u
u=-(100x0.0005+1)
-1.05
m/s
6000J
E=Fxd
E/d=F
F=6000/30
200
N
Half – Work done = force x distance moved, the
force stays the same but the distance is half,
so she would do half as much work.
P2 Topic 4: Momentum energy work and power
Friday, 13 March 2015
Additional Science Revision
Model Answers
50 000J – She has converted her GPE into Kinetic
Energy.
watts
Work done
Power = Work Done / Time taken
W
P2 Topic 4: Momentum energy work and power
Friday, 13 March 2015
Additional Science Revision
Model Answers
7.2x104J
10s
P=E/t
GPE=mgh
P=7.2x104/10
W
7.2x103
120s
1.5x106W
P=E/t
Pxt=E
E=1.5x106x120
1.8x106
J
75kg
200m
10N/kg
GPE=mgh
4.0x105kg
GPE=mgh
GPE/mg=h
10N/kg
1.54x105W
6400 N
1.3x105m
J
E=Fxd
E=6400x1.3x105
8.32x106
J
P=E/t
t=E/P
t=8.32x106/1.54x105
9.85x108
s
2.0x1010kg
1.2m
10N/kg
8.16J
GPE=75x10x200
1.5x105
J
h=2.0x1010/(4.0x105x10)
5.0x103
m
GPE=mgh
GPE/gh=m
m=8.16/(10x1.2)
0.68
kg
P2 Topic 4: Momentum energy work and power
Friday, 13 March 2015
Additional Science Revision
Model Answers
KE=½mv2
J
gravitational potential
300kg
15m/s
33750
kinetic
KE=½x300x152
33750
200kg
4000
KE=½mv2
J
KE=½mv2
√(2KE/m)=v
√(2x33750/200)=v
18.4
m/s
8.16J
8.16J
0.68kg
KE=½mv2
√(2KE/m)=v
√(2x8.16/0.68)=v
4.90
m/s
P2 Topic 4: Momentum energy work and power
Friday, 13 March 2015
Additional Science Revision
Model Answers
1000kg
KE=½mv2
1000kg
15m/s
KE=½x1000x152
30m/s
8000N
112 500
E=Fxd
J
8000N
E/F=d
112500/8000=d
14.06
m
KE=½mv2
KE=½x1000x302
450 000
E=Fxd
J
E/F=d
450000/8000=d
56.25
m
The amount of kinetic
energy depends on v2.
Doubling the velocity,
requires 4x the
energy. Having 4x the
energy will require 4x
the distance to stop.