PHY101 Assignment 1 solution spring 2017

Question No 1.

**a) In an elastic collision between two particles, does the kinetic energy of each particle change as a result of the collision?**

Ans: In a one-dimensional collision between two identical particles with the same initial speed, the kinetic energy of the particles will not change.

**b) Three balls are thrown into the air simultaneously. What is the acceleration of their center of mass while they are in motion?**

Ans: The acceleration of their center mass will 9.8 m/s².

**c) The Moon revolves around the Earth. Model its orbit as circular. Is the Moon’s linear momentum conserved? Is its kinetic energy conserved?**

Ans: No an external force of gravity acts on the moon. Yes, because its speed is constant

Question No 2.

**a) Does a large force always produce a larger impulse on an object than a smaller force does?**

**Explain?**

Ans: It is possible for an object to obtain a larger impulse from a smaller force than it does from a larger force. Impulse is the product of both net force and time. A large impulse could be obtained from a small force if the small force acts for a long period of time.

**b) When a particle rotates in a circle, a force acts on it directed toward the center of rotation. Why is it that, this force does no work on the particle?**

Ans: Since at any point along the circle the centripetal force is perpendicular to the velocity v and therefore to the displacement dr, the scalar product dW = F·dr is zero therefore this force does not work on it.

**Question. No: 3**

**A number of sphere of pure (Pb) are found to have a mass of 13.56grams. The lead (Pb) is then placed into graduated cylinder containing 3.0 millimeters of water, and the water is displaced to the level shown in the diagram. Which statement below is true?**

Ans: b) The lead has a volume of 1.2 millimeters and a density of about 11g/ml.

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