Department of Mathematics and Natural Sciences
PHY111 - Principles of Physics-I (Spring 2021)
Assignment-2
Total Marks: 30
Answer all three questions.
1. A 75.0 kg man stands on a platform scale in an elevator. Starting from rest, the elevator
ascends, attaining its maximum speed of 1.20 m/s in 1.00 s. It travels with this constant speed for
the next 10.00 s. The elevator then undergoes a uniform acceleration in the negative y direction
for 1.70 s and comes to rest. What does the scale register:
(a) before the elevator starts to move? (1 mark)
(b) during the first 1.00 s? (3 marks)
(c) while the elevator is traveling at constant speed? (2 marks)
(d) during the time it is slowing down? Take g = 10 ms-2. (4 marks)
2. Box 1, a wooden box, has a mass of 8.60 kg
and a coefficient of kinetic friction with the
inclined plane of 0.35. Box 2, a cardboard box,
sits on top of box 1. It has a mass of 1.30 kg.
The coefficient of kinetic friction between the
two boxes is 0.45. The two boxes are linked by
a rope which passes over a pulley at the top of
the incline, as shown in the diagram. The inclined plane is at an angle of 38.0° with respect to the
horizontal.
(a) What is the acceleration of each box? (7 marks)
(b) Now consider all surfaces are frictionless. Then calculate the amount of force with direction
to prevent the sliding of the boxes. (3 marks)
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3. An amusement park ride consists of a large vertical cylinder that
spins about its axis fast enough such that any person inside is held
up against the wall when the floor drops away. The coefficient of
static friction between person and wall is 0.25 and the radius of the
cylinder is 7m.
(a) How many minimum revolutions per minute does the cylinder
make? (5 marks)
(b) Calculate the angular velocity and frequency of the motion at
this condition. (2 marks)
(c) What is the effect of the mass of the person on the time period,
radial acceleration and tangential acceleration. (3 marks)
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