University of Papua New Guinea
School of Natural and Physical Science and UPNGOC
Physics Division
Assignment #2 (___/42)
External SFY - Semester 1, 2023
Question 1. Force and Tension
(i)
Refer to the figure below and solve for T1 and T2. (6 marks)
(ii)
Block A of 150N rests on a frictionless inclined plane of slope 30◦. A flexible cord
attached to block A passes over a frictionless pulley and is connected to block B of
weight W. Find the weight W for which the system is in equilibrium. (6 marks)
Question 2. Force and Motion
A hockey puck with mass 0.2kg is at rest at the origin (x = 0) on the horizontal, frictionless
surface on the rink. At time t = 0 a player applies a force of 0.25N to the puck, parallel to the xaxis; he continues to apply this force until t = = 2.00s.
(a) What are the position and speed of the puck at t = 2.00s? (3 marks)
(b) If the same force is again applied at t = 5.00s, what are the position and speed of the puck
at t = 7.00s? (5 marks)
Question 3. Momentum
Spheres A (mass 0.02kg), B (mass = 0.03kg) and C (mass = 0.05kg) are approaching the origin
as they slide on a frictionless air table. See figure below.
The initial velocities of A and B are given in the figure. All three spheres arrive at the origin at
the same time and stick together.
(a) What must the x- and y- components of the initial velocity of sphere C be if all three
objects are to end up moving at 0.5m/s in the +x direction after the collision? (5 marks)
(b) If sphere C has the velocity found in part (a), what is the change in kinetic energy of the
system of the three spheres as a result of the collision? (5 marks)
Question 4. Circular and Rotational motion with Work and Energy Theorem.
a) A small bead can slide without friction on a circular hoop that is in a vertical plane and
has a radius of 0.100m. The hoop rotates at a constant rate of 4.00rev/s about a vertical
diameter. See figure below.
(i) Find the angle β at which the bead is in vertical equilibrium. (6 marks)
(ii) Is it possible for the bead to ride at the same elevation as the center of the hoop?
Elaborate on your answer.
(iii)What will happen if the hoop rotates at 1.00rev/s? (6 marks)
b) The gravitational pull of the earth on an object is inversely proportional to the square of
the distance of the object from the center of the earth. At the earth’s surface, this force is
equal to the objects normal weight mg, where g = 9.8m/s2, and at large distances, the
force is zero. If a 20,000kg asteroid falls to earth from a very great distance away, what
will it be its maximum speed as it strikes the earth’s surface, and how much kinetic
energy will impact to our planet? You can ignore the effects of the earth’s atmosphere.