Transcript 2. - Uplift Education

1.
An object falls freely from rest through a vertical distance of 44.0 m in a time
of 3.0 s. What value should be quoted for the acceleration of free-fall?
A. 9.778 m s-2
B. 9.780 m s-2
C. 9.78 m s-2
D. 9.8 m s-2
D.
Multiplication or division:
(3sig.fig.)x(2sig.fig) = 2sig.fig
(3sig.fig.)/(2sig.fig) = 2sig.fig
2. What is the order of magnitude for the frequency of visible light?
A. 10–15 Hz
Either you know visible light
frequency range, or you know
visible light wavelength range:
B. 10–7 Hz
C. 109 Hz
D. 1015 Hz
D.
400 nm → 0.75x1015 Hz
700 nm → 0.43x1015 Hz
and then use 𝑐 =f
3. A woman walks due north at 1 m s–1 before turning through an angle of 900 to
travel due east without any change in speed. What is the change, if any, of her
velocity?
A. No change
𝑣2
B. 1ms–1 to the west
C.
2 ms–1 to the north east
D.
2 ms–1 to the south east
𝑣1
D.
∆𝑣 = 𝑣2 − 𝑣1 = 𝑣2 + (−𝑣1 )
𝑣2
∆𝑣
−𝑣1
5. A parachutist jumps out of an aircraft and falls freely for a short time,
before opening his parachute. Which graph shows the variation of the
acceleration a with time t of the parachutist from the time he leaves the
aircraft until after the parachute is completely open?
A.
B.
B.
C.
D.
Before the parachute opens
1. When the skydiver jumps out of the
plane he accelerates due to the force of
gravity pulling him down.
2. As he speeds up the upwards air
resistance force increases. He carries on
accelerating as long as the air resistance is
less than his weight.
3. Eventually, he reaches his terminal
speed when the air resistance and weight
become equal.
After the parachute opens
4. When the parachute opens it has a large surface area which increases the air resistance. The force of air
resistance becomes much, much greater than the force of gravity. The net force on the descending skydiver
now has an acceleration that points upward - negative acceleration or deceleration. Gradient becomes strongly
negative when the parachute is opened. This causes a rapid decrease in the skydiver's velocity.
5. As the parachutist slows down, his air resistance gets less until eventually it equals the downward force of
gravity on him (his weight). Once again the two forces are equal and he falls at terminal speed. This time it's a
much slower terminal speed than before.
B.
𝑚𝑣𝑓
_ 𝑚𝑣𝑖
=
𝑚𝑣𝑓
+
_𝑚𝑣𝑖
=
Or one can decompose both vectors into components (easier)
1. Horizontal components will be the same so result of subtraction is zero.
2. Final vertical component – initial vertical component is equal to 2×(final vertical component)
D.
As the block is pulled with greater and greater force, but still doesn’t
move, form Newton’s first law it is obvious that static frictional force
increases. It is maximum at the moment, when the block starts to move:
𝑚𝑎𝑥
𝑠𝑡𝑎𝑡𝑖𝑐 𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑓𝑜𝑟𝑐𝑒: 𝐹𝑓𝑟 ≤ 𝜇𝑠 𝐹𝑛 → 𝐹𝑓𝑟
= 𝜇𝑠 𝐹𝑛
Once the block starts to move, kinetic friction takes over. It is
constant force (𝐹𝑓𝑟 = 𝜇𝑘 𝐹𝑛 , but 𝜇𝑘 > 𝜇𝑠 )
8. The pound is a unit of mass equivalent to 0.454 kg. It is used in a limited number of
countries but is rarely used by modern scientists. Which statement is correct?
A. Scientists cannot be sure that all other scientists will be able to work in pounds.
B. The pound cannot be defined precisely enough to be used.
C. The pound is too large a unit to be used for most masses.
D. The pound cannot be divided into metric portions.
Everything can be converted into metric system. Just divide by 10, then again by ten…..
A.
D.
𝑀 + 𝑚 𝑣 = 𝑀𝑉
→ 𝑉=
𝑀+𝑚
𝑣
𝑀
C.
𝑐=
𝑒𝑛𝑒𝑟𝑔𝑦 𝑝𝑜𝑤𝑒𝑟 ∙ 𝑡𝑖𝑚𝑒 12 (200 − 0)
200
=
=
×
= 60
= 2000 𝐽 𝑘𝑔−1 𝐾 −1
𝑚 ∙ ∆𝜃
𝑚 ∙ ∆𝜃
0.2 (26 − 20)
6
B.
C.
It is not in SL curriculum – but one never knows.
In the case of changing P(V), work is the area
bellow graph p(V):
13. The diagram shows a simple pendulum undergoing simple harmonic motion
between positions X and Z. Y is the rest position of the pendulum.
𝐹 = −𝑚𝑔 𝑠𝑖𝑛𝜃
Which describes the magnitude of linear acceleration
and linear speed for the pendulum bob?
v=0
v=0
v = vmax
𝑎 = 𝑎𝑚𝑎𝑥 →
𝐹 = 𝐹𝑚𝑎𝑥 →
A.
B.
C.
D.
Linear acceleration
zero at Y
maximum at X and Z
maximum at X and Z
zero at X and Z
Linear speed
zero at Y
B.
zero at X and Z
maximum at X and Z
maximum at X and Z
𝑎=0
𝐹=0
𝑎 = 𝑎𝑚𝑎𝑥 ←
𝐹 = 𝐹𝑚𝑎𝑥 ←
linear means along the arch
14. Some of the properties that can be demonstrated using waves are
I. refraction
II. polarization
III. diffraction.
Which properties can be demonstrated using sound waves?
A. I and II only
B. I and III only B.
C. II only
D. III only
polarization happens only with
transverse waves, and sound is
longitudinal wave
15. The amplitude of a wave at a certain distance for a source is A and its
intensity is I. At this position the amplitude increases to 4A. What is the
intensity of the wave?
A. I
B. 2I
𝐼=
C. 4I
D. 16I
D.
𝑃
4𝜋𝑑 2
power is 𝑒𝑛𝑒𝑟𝑔𝑦 × 𝑡𝑖𝑚𝑒.
Energy is proportional to amplitude squared.
Intensity is proportional to amplitude squared.