Chung Cheng Yishun
0-LEVEL PRELIMINARY EXAMINATION
PHYSICS 6091 PAPER 2- SUGGESTED ANSWERS
1(a)(i)
The car travelled at constant speed at 30 m/s from t = 0 to 50 s, then decelerates uniformly from t =
50 s to 70 s until it comes to rest. Next the car remains stationary / at rest for a further 10 s.
It then reverses in direction and accelerates uniformly from 80 to 90 s in the negative direction
before decelerating uniformly to rest from 90 to 110 s.
(ii)
Either, by graphical method
30
Retardation = Gradient of v-t graph = 70−50 = 1.5 𝑚 𝑠 −2
Or, using formula,
𝑣−𝑢
0−30
a=
=
= −1.5 𝑚 𝑠 −2
𝑡
20
2(a)
2(c)
3(a)
Velocity increases at a decreasing rate until it becomes constant.
Acceleration decreases until it becomes zero.
There are an extremely large number of gas molecules in the cylinder and statistically, they
will exert the same average force on unit area of the inner wall with equal probability.
These collisions exert a force per unit area that is constant at all parts of the inner wall.
Majority of candidates are confused between intermolecular collisions and collisions against
inner wall surfaces.
Note that the frequency of collision of the air molecules with the inner wall is not the same.
3(b)
4(a)
4(b)
5(a)(i)



Speed of gas molecules decrease and they move less vigorously.
They hit inner walls with small force and less frequently.
Smaller force exerted per unit area on inner walls (smaller pressure)
Most candidates did not mention molecules hitting the inner walls less hard. (with less force).
Molecules of seawater will slide over each other at a faster speed.
• Molecule seawater move more vigorously
• Molecules of seawater move farther apart from each other
Large majority of candidates focused their answer on steam molecules losing heat instead of
seawater molecules gaining heat. Some candidates wrote about heat transfer methods.
Q = mcΔ𝜃
2.65 x 108 = m (3900)(64-30)
Mass = 1998.5 ≈ 2000 kg
angle A= 42 o and angle B = 30 o
(nearest degree for angle)