14-16 sample answers drawn from a number of different
files
Questions are shown in black type with the answers in
bold blue1. What is meant by the velocity of a body?
The velocity of an object is its speed in a certain
direction2. What can authorities do to minimise the loss of life due to
the catastrophic effects of the movement of a tectonic plate?
warning devices, better buildings that can withstand earthquakes,
international cooperation in research. Limit the development of centres of population
in areas of known high risk
3. What happens to the temperature of a
resistor when an electric current passes through it?
it goes up (increases, rises)
4. What causes this change of
temperature?
The atoms of the resistor vibrate more
strongly and the electrons collide more often with each other and with the atoms of
the resistor. 5. Calculate the power in each of the following
cases:
(a) a 12 V car battery supplying 100 A
Power = voltage x current = 12 x 100 = 1200 W = 1.2
kW
6. A 2000 kg car travelling at 10 m/s brakes
steadily to a stop in 5 seconds.
(a) calculate the kinetic energy of the car before
it brakes and,
(b) after it has stopped.
(c) calculate the acceleration of the
car.
(d) what is the force exerted by the brakes?
(e) calculate the energy
changes in the brakes and describe these changes in words.
(a) Kinetic energy = ½ mv2 = ½ x 2000 x 102 = 100 000 J
(b) 0 it is not
moving!
(c) Acceleration = change in speed/time = 10/5 = 2 m/s2
(d) Force =
mass x acceleration = 2000 x 2 = 4000 N
(e) Energy changes in the brakes is an
increase of 100 000 J if all the car's kinetic energy is assumed to be transferred to the
brakes. Kinetic energy is converted into heat energy with some sound.
7. A 250 kg sledge travels down a slope, falling a vertical distance of
20 m and reaching a speed of 18 m/s at the bottom.
(a) how much potential energy did it
loose
(b) how much kinetic energy did it gain
(c) how much energy was converted
to heat and sound
(a) Gravitational potential energy (GPE) =
250x10x20 = 50 000 J
(b) K.E = 0.5x250x182 = 40 500 J
(c) Energy converted to
heat and sound = 50 000 40 500 = 9500 J
8. Caesium 137 was
a major problem after the Chernobyl accident in 1986. When will the amount of caesium in
any fallout material have reached one quarter of its original activity?
(Half life of
caesium 137 = 28 years)
after 56 years, after two half lives,
in 2042
..
9. Some time in the distant future the Sun will expand to
become a large star called a
Red
Giant
with a core that is "burning" heavier elements such as
helium
10. What is the voltage difference across a
piece of wire of resistance 100 ? with a current of 20 mA flowing through
it?
v
oltage difference = current x resistance
= 0.02x100 = 2 V
11. Write down EIGHT points that
should be remembered when plotting a graph.
1. Give your
graph a title
2. Chose a sensible scale for both axes
3. Try and draw a graph
that will fill the graph paper
4. Label the axes
5. Put units on both axes
6.
Plot the points correctly
7. Mark the points clearly + or
8. Draw a smooth best
fit line through the points. This is often called a trend line. It shows the general trend
but you do not have to join up all the points in fact you should not do this unless
they actually fit the trend line.
9. Recognise any anomalous points (ones that are
way off the general trend).
10. Draw the line clearly and
finely12. What happens to the intensity of all signals as they travel
further from the transmitter?
it gets
less
.
..
13. As the signal travels it may pick up random additions
to the original signal which reduce its quality. These random additions are called
noise
..
14. How does the transfer of
heat energy by conduction differ from the way heat energy is transferred by
convection?
in conduction the particles vibrate about a
fixed position while in convection the whole fluid moves. Note that in metals the
electrons aid conduction by drifting from the hot end of a rod to the cold
end.
.
15. Use the ideas of momentum and momentum
conservation to explain:
(a) why it would be really painful to play baseball with a metal
bat
(b) why the recoil velocity is less if you hold a rifle against your shoulder as you fire
it
(c) why heavy rain is much more painful than light rain
(d) how a boy who is
standing on perfectly frictionless ice in the middle of a skating rink could get to the edge
(a) very short stopping time for the ball so large force on the
hands via the bat
(b) recoil mass is that of the rifle PLUS that of your body so
recoil velocity is less
(c) larger mass and faster terminal speed
(d) throw
something in the opposite direction
