C9.1 Momentum and impulse AQA AS Physics C9 Force And Momentum Kerboodle Answers: Page No. 157
1.Ans- a
i 1.2 x 10-18 kgms-1
ii0.050kgms-1
iii 14kgms-1
b i 6.0kg
ii
20ms-1
2.Ans-
a 3.6 x 105 kgms-1
b 60s
3.Ans-
a 5.4 x 106 kgms-1
b 45 s
4.Ans-
a9.0 x 103 kgms-1
b i -8.4 x 103 kg ms-1
ii 1.0 ms-1
9.2 Impact forces AQA AS Physics C9 Force And Momentum Kerboodle Answers: Page No. 160
1.
a the initial momentum of the lorry
1600kg ms-1
b the force of the impact.
3200N
2.
a the change of momentum of the car due to the impact
3000kgms-1
b the impact force.
7.5kN
3.
a the change of momentum
-4.2 x 10-23 kgms-1
b the force on the molecule.
-1.9 x 10-13 N
4.
-2.1 x 10-23 kgms-1
9.3 Conservation of momentum AQA AS Physics C9 Force And Momentum Kerboodle Answers : Page No. 163
1.
0.72 m s-1
2.
0.7ms-1 in the same direction
3 .
0.05 m s-1 in the direction the 1.0 kg trolley was l 1.0 x 107m2 moving in
4.
-0.63 m s-1 in the opposite direction to its initial direction.
9.4 Elastic and inelastic collisions AQA AS Physics C9 Force And Momentum Kerboodle Answers: Page No. 165
1.a i it rebounds to the same height
ii it rebounds to a lesser height. In aii, the ball is released from a height of 1.20m above the surface and it rebounds to a height of 0.90 m above the surface. Show that of its kinetic energy is lost in the impact,
2.
a the velocity of the vehicles immediately after impact
9.0ms-1 in the same direction
b the loss of kinetic energy due to the impact.
24kJ
3.a the speed and direction of the 1.0 kg ice puck after the collision
1.1 ms-1 in the reverse direction
b the loss of kinetic energy due to the collision.
20J
4.
a’i 1.0 ms-1
ii Show that the collision was an elastic collision.
b The driver of the 250kg car experiences a force from his/her car which slows him/her down; the other driver experiences a force from his/her car that accelerates him/her.
9.5 Explosions AQA AS Physics C9 Force And Momentum Kerboodle Answers : Page No. 167
1 .0.35 ms-1
2.
a 0.25ms-1 ;the mass of A and X was greater 1 than the mass of B. so B moved away faster.
b Show that the mass Of X must have been 0.10 kg.
3.
a i 0.10 ms-1
ii15 mJ
b 0.19ms-1
4.a the speed at which the rock was thrown from the boat
9.0ms-1
b the kinetic energy gained by
i the boat
1.1 J
ii the rock.
81 J
Practice questions: Page No. 168-169
1. (a)In an inelastic collision, kinetic energy is not conserved
(b) (i) the momentum of the ball before the collision
Momentum p = mv gives
p = 0.12 × 18 = 2.16 N s (or kg m s-1)
(ii) the momentum of the ball after the collision
p = 0.12 × (−15)
= −1.8 N s (or kg m s-1 )
(iii) the total change of momentum of the ball
Change in momentum = 2.16 − (−1.8)
= 3.96 N s (or kg m s-1 )
(iv) the average force acting on the ball during contact With the bat
(v) the kinetic energy lost by the ball asa result 01 the collision.
2 .
(a)
(b)
Impulse = change of momentum
∴0.135 = mA × 0.60
from which mA = 0.225 kg or 0.22 kg or 0.23 kg
(c) The final total momentum of the system is zero
3.(a) Calculate the momentum of the engine.
p = mv = 6.2 × 104 × 0.35
= 2.17 × 104 N s (or kg m s−1 )
or 2.2 × 104 N s
(b) Initial momentum of engine = combined momentum after coupling
∴2.17 × 104 = 10.2 × 104 v
gives v = 0.213 m s-1 or 0.21 m s-1
4. (a) )
Two quantities that are conserved:
• momentum
• kinetic energy
(b) A gas molecule makes an elastic collision with the walls of a gas cylinder.
The molecule is travelling at 450ms—l at right angles towards the wall before the
(i)
Magnitude of velocity is 450 m s−1
The direction is away from the wall at 90 ° to it (or in the opposite direction to the initial velocity).
(ii)
(c)
• Force is exerted on the molecule by the wall
• Molecule experiences a change in its momentum
• Molecule must exert a force on the wall which is equal and opposite to the force produced by the wall on the molecule, by Newton’s third law of motion
5.(a)
b (i)
(ii)
6
(a) The shaded area represents impulse (or change in momentum).
(b)
7.(a) The total momentum of a system of objects remains constant provided that no external resultant force acts on the system
(b) (i)
(ii)
(iii)
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