PHYS 1103: General Physics I
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Assignment 3: Energy and Momentum (6%)
Total marks for this assignment: 20
Once you have completed Unit 3, please submit Assignment 3 using the assignment
submission tool in Moodle so that your Open Learning Faculty Member can grade it
and provide you with feedback. This assignment covers material from chapters 5
and 6.
1. Many mountain roads are built so that they spiral around the mountain
rather than go straight up toward the peak. Discuss this design from the
viewpoint of energy and power. (1 mark)
2. What is the work-energy theorem? To what fundamental principle of physics
does it relate? (1 mark)
3. In trying to lift sandbag B, attached to a lightweight rope as in the figure
below, a worker at the top of the scaffolding places his tools and lunch kit
into box A so that the entire mass of box A is now 80 kg. If the sandbag is
65 kg, find its speed as it hits the scaffolding. Assume that the sandbag starts
from rest, and that the pulleys have negligible mass and friction. (2 marks)
4. A 6.00 kg object is lifted vertically through a distance of 5.25 m by a light
string under a tension of 80.0 N. Find: (2 marks)
a. The work done by the force of tension,
b. The work done by gravity, and
c. The final speed of the object if it starts from rest.
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Assignment 3
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5. A train of mass 2.4 × x10 kg enters a 5.0 km stretch of track with a vertical
rise of 40 m at a speed of 1.0 m/s and leaves at 3.0 m/s. Assuming that
frictional drag is negligible: (3 marks)
a. Define and find a value for each term in the equation Wnc = ΔKE + ΔPE.
b. Find the average mechanical power delivered by the engine for the climb
if it is done at constant acceleration.
6. When a sprinter bursts from the starting blocks at the start of a race, he/she
generates considerable forward momentum. Is this an example where
momentum is not conserved? Explain. (1 mark)
7. A 5.00 g object moving to the right with a speed of 20.0 cm/s makes an elastic
head-on collision with a 10.0 g object initially at rest. Find: (3 marks)
a. The velocity of each object after the collision.
b. The fraction of the initial energy transferred to the 10.0 g object.
8. An 8.0 g bullet is fired into a 2.5 kg ballistic pendulum and becomes
embedded in it. If the pendulum rises a vertical distance of 6.0 cm, calculate
the initial speed of the bullet. (3 marks)
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9. A locomotive of mass 2.1 × 10 kg travelling at 2.0 m/s runs into an identical
stationary locomotive. (4 marks)
a. If the collision is perfectly inelastic, what is the speed of the two trains
after the collision?
b. If the collision is perfectly inelastic, what fraction of the energy is lost after
the collision?
c. If the collision is perfectly elastic, find the motions of the locomotives after
the collision.
d. If the collision is perfectly elastic and lasts for 1.5 s, find the average force
exerted on the stationary locomotive during the collision.
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