PHY101 Assignment 1 Solution Spring 2017

Physics - PHY101 Assignment 1 Solution - Semester: 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?
Answer: No, the kinetic energy is conserved in an elastic collision. 

b) Three balls  are  thrown  into  the  air  simultaneously.  What  is  the  acceleration  of  their  center  of mass while they are in motion?
Answer: As the acceleration will be due to gravity, so it will be 9.8 m/s^2.

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

Answer: Linear momentum will change as the direction in circular motion keeps changing. Kinetic energy will be conserved as K.E = 1/2mv^2. 

Question. No: 2

a) Does a large force always produce a larger impulse on an object than a smaller force does? Explain
Answer: No a larger force does not always produce a larger impulse. Impulse is defined as net force applied times the length of time over which that force is applied = F(delta)t. So if a larger force is applied for a shorter time, it will not necessarily  be greater than a smaller force applied for a longer 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?
Answer: In centripetal force the direction of velocity is perpendicular to the direction of force, and as work done W=Fdcos(theta), and cos90 = 0, so W = 0 and hence no work is done. 

Question. No: 3
A  number of sphere of pure (Pb) are found to have a  mass of 13.56 grams. 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?

a) The lead has a volume of 4.2 millimeters and a density of about 3.2 g/ml.
b) The lead has a volume of 1.2 millimeters and a density of about 11 g/ml.
c) The lead has a volume of 4.4 millimeters and a density of about 3.1 g/ml.
d) The lead has a volume of 1.4 millimeters and a density of about 9.7 g/ml.
e) The volume of the lead cannot be determined because the water level in the graduated cylinder is curved.

Answer: Correction option is b.
Explanation: As we can see from the figure, volume level increases from 3.0 millimeters to 4.2 millimeters, so volume of lead is 4.2 - 3 = 1.2 millimeters. And formula to calculate density is D = m/v, so 13.6/1.2 = 11.3 g/ml.

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