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Name: ______________________
1.
IB Physics 11 – Work, Energy & Momentum
December 19th, 2013
A brother and sister take the same time to run up a set of steps. The sister has a greater mass than her brother.
Which of the following is correct?
Has done the most work
Has developed the greatest power
A.
brother
brother
B.
brother
sister
C.
sister
brother
D.
sister
sister
(Total 1 mark)
2.
A nuclear power station produces 10 GW of electrical power. The power generated by the nuclear reactions in the
core of the reactor is 25 GW. The efficiency of the power station is
A.
15 %.
B.
35 %.
C.
40 %.
D.
60 %.
(Total 1 mark)
3.
Which of the following is equivalent to the principle of energy conservation?
A.
Newton’s first law
B.
The first law of thermodynamics
C.
Newton’s second law
D.
The second law of thermodynamics
(Total 1 mark)
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4.
The graph shows the variation with force F of the extension s of a spring.
The work done in changing the extension of the spring from 3.0 cm to 6.0 cm is
A.
15 N cm.
B.
30 N cm.
C.
45 N cm.
D.
60 N cm.
(Total 1 mark)
5.
Two objects undergo an inelastic collision. Which of the following is correct in respect of both the conservation of
momentum and the conservation of total energy of the system?
Momentum
Total energy
A.
conserved
not conserved
B.
conserved
conserved
C.
not conserved
not conserved
D.
not conserved
conserved
(Total 1 mark)
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6.
Which of the following is a correct definition of work?
A.
Product of force and distance
B.
Product of force and distance moved in the direction of the force
C.
Product of power and time
D.
Product of force and displacement
(Total 1 mark)
7.
A ball is thrown vertically upwards and comes down again. Air resistance is negligible. Which of the following
graphs shows how the gravitational potential energy EP varies with time t?
(Total 1 mark)
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8.
A ball falls vertically and bounces off the ground. Immediately before impact with the ground the speed of the ball
is u. Immediately after leaving the ground the speed is v.
Which of the following expressions is the ratio of
A.
v
u
B.
1
C.
v
 
u
D.
v
1  
u
kinetic energy lost on collision
?
kinetic energy immediatel y before collision
v
u
2
2
(Total 1 mark)
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9.
A tennis ball of mass m moving horizontally with speed u strikes a vertical tennis racket. The ball bounces back
with a horizontal speed v.
The magnitude of the change in momentum of the ball is
A.
m(u + v).
B.
m(u – v).
C.
m(v – u).
D.
zero.
(Total 1 mark)
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10.
A gas atom strikes a wall with speed v at an angle θ to the normal to the wall. The atom rebounds at the same speed
v and angle θ.
Which of the following gives the magnitude of the momentum change of the gas atom?
A.
zero
B.
2mv sinθ
C.
2mv
D.
2mv cosθ
(Total 1 mark)
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11.
Two carts of different mass m and M are connected by a spring. They are pushed together such that the spring is
compressed.
After the carts are released, the cart of mass m moves with velocity v. The change in the momentum of mass M is
A.
mv.
B.
–mv.
C.
Mv.
D.
–Mv.
(Total 1 mark)
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12.
A rubber ball, travelling in a horizontal direction, strikes a vertical wall. It rebounds at right angles to the wall. The
graph below illustrates the variation of the ball’s momentum p with time t when the ball is in contact with the wall.
Which of the following statements is true?
A.
The shaded area is equal to the force exerted by the wall on the ball.
B.
The shaded area is equal to the force exerted by the ball on the wall.
C.
The gradient is equal to the force exerted by the wall on the ball.
D.
The gradient is equal to the force exerted by the ball on the wall.
(Total 1 mark)
13.
Two spheres of masses m1 and m2 are moving towards each other along the same straight-line with speeds v1 and v2
as shown.
The spheres collide. Which of the following gives the total change in linear momentum of the spheres as a result of
the collision?
A.
0
B.
m1v1 + m2v2
C.
m1v1 − m2v2
D.
m2v2 − m1v1
(Total 1 mark)
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14.
This question is about impulse.
(a)
A net force of magnitude F acts on a body. Define the impulse I of the force.
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(1)
(b)
A ball of mass 0.0750 kg is travelling horizontally with a speed of 2.20 m s–1. It strikes a vertical wall and
rebounds horizontally.
Due to the collision with the wall, 20 % of the ball’s initial kinetic energy is dissipated.
(i)
Show that the ball rebounds from the wall with a speed of 1.97 m s–1.
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(2)
(ii)
Show that the impulse given to the ball by the wall is 0.313 N s.
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(2)
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(c)
The ball strikes the wall at time t = 0 and leaves the wall at time t = T.
The sketch graph shows how the force F that the wall exerts on the ball is assumed to vary with time t.
The time T is measured electronically to equal 0.0894 s.
Use the impulse given in (b)(ii) to estimate the average value of F.
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(4)
(Total 9 marks)
15.
This question is about forces.
An athlete trains by dragging a heavy load across a rough horizontal surface.
The athlete exerts a force of magnitude F on the load at an angle of 25° to the horizontal.
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(a)
Once the load is moving at a steady speed, the average horizontal frictional force acting on the load is 470 N.
Calculate the average value of F that will enable the load to move at constant speed.
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(2)
(b)
The load is moved a horizontal distance of 2.5 km in 1.2 hours.
Calculate
(i)
the work done on the load by the force F.
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(2)
(ii)
the minimum average power required to move the load.
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(2)
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(c)
The athlete pulls the load uphill at the same speed as in part (a).
Explain, in terms of energy changes, why the minimum average power required is greater than in (b)(ii).
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(2)
(Total 8 marks)
16.
This question is about power and efficiency.
A bus is travelling at a constant speed of 6.2 m s–1 along a section of road that is inclined at an angle of 6.0° to the
horizontal.
(a)
(i)
The bus is represented by the black dot shown below. Draw a labelled sketch to represent the forces
acting on the bus.
●
(4)
(ii)
State the value of the rate of change of momentum of the bus.
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(1)
(b)
The total output power of the engine of the bus is 70 kW and the efficiency of the engine is 35 %. Calculate
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the input power to the engine.
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(2)
(c)
The mass of the bus is 8.5 × 103 kg. Determine the rate of increase of gravitational potential energy of the
bus.
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(3)
(d)
Using your answer to (c) and the data in (b), estimate the magnitude of the resistive forces acting on the bus.
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(3)
(Total 13 marks)
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17.
This question is about collisions.
(a)
State the principle of conservation of momentum.
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(2)
(b)
In an experiment, an air-rifle pellet is fired into a block of modelling clay that rests on a table.
(not to scale)
The air-rifle pellet remains inside the clay block after the impact.
As a result of the collision, the clay block slides along the table in a straight line and comes to rest. Further
data relating to the experiment are given below.
Mass of air-rifle pellet
Mass of clay block
Velocity of impact of air-rifle pellet
Stopping distance of clay block
(i)
= 2.0 g
= 56 g
= 140 m s–1
= 2.8 m
Show that the initial speed of the clay block after the air-rifle pellet strikes it is
4.8 m s–1.
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(2)
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(ii)
Calculate the average frictional force that the surface of the table exerts on the clay block whilst the
clay block is moving.
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(4)
(c)
Discuss the energy transformations that occur in the clay block and the air-rifle pellet from the moment the
air-rifle pellet strikes the block until the clay block comes to rest.
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(3)
(d)
The clay block is dropped from rest from the edge of the table and falls vertically to the ground. The table is
0.85 m above the ground. Calculate the speed with which the clay block strikes the ground.
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(2)
(Total 13 marks)
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