PHY101 Physics Assignment 2 Solution Fall 2012

Question # 1

In one experiment, a red wagon at rest is pushed to the left with a force of 150N for 1.0s. In a
second experiment a blue wagon with the same mass as the red wagon is pushed from rest to the
left with a force of 150N for 2.0s. Which statement below is true? Marks = 7
(3+4)
a) The red wagon had a smaller impulse but a larger change in momentum than the blue.
b) The red wagon had a smaller impulse and a smaller change in momentum than the blue.
c) The red wagon had a same impulse and a same change in momentum as the blue.
d) The red wagon had a larger impulse but a smaller change in momentum than the blue.
e) The red wagon had the same impulse but a larger change in momentum than the blue.
*Write the reason of your above selected choice as well.Physics (PHY101) VU of Pakistan
Question # 2
The light’s wavelength is 6.0×10 -7 m. The light completes 5.0 cycles in 10 -14 seconds. What is  the light’s wave speed? Marks = 5
Question # 3
A person takes a 2.0Kg mass and lifts it 0.50m above a table that is itself 1.0m above the floor.
The person then moves the mass 1.0m to the side so that it is directly over the floor, 1.50m
below. Which statement is true? Marks 7 (2+5)
a) The mass has 30.0J of Gravitational Potential Energy (GPE) relative to the floor.
b) The person did 10.0J of work in lifting the mass.
c) The mass has 10.0J of Gravitational Potential Energy (GPE) relative to the table.
d) The person did not work against gravity when moving the mass 1.0m to the side.
e) All of the above are true.
*Write the reason of your above selected choice as well.

Solution:

Reason:

a) Energy relative to Floor =PE=mgh=2×9.8×1.5=30Joule(consider 9.8=10)

b)Person work done against the gravity in lifting=PE=mgh=2x10xx0.5)=10Joule (g=10m/s^2)

c)Energy possess relative to table =PE=mgh=2x10x0.5=10Joule

d)In physics he did not any waork against gravity while moving to side.

e) All of above is correct answer

Question # 4
If an object on a horizontal, frictionless surface is attached to a spring, displaced, and then
released, it will oscillate. If it is displaced 0.120 m from its equilibrium position and released
with zero initial speed, then after 0.800 s its displacement is found to be 0.120 m on the opposite
side, and it has passed the equilibrium position once during this interval.
Find (a) the amplitude; (b) the period; (c) the frequency. Marks = 6

Solution:

a)When object moved 0.120m from its equilibrium position say to the right. Then after 0.800 sec it has passed through its equilibrium position and reached to the opposite side at 0.120 m from equilibrium. Then it has covered 0.240 m to reach to the other end.(0.120+0.120)

therefore amplitude is 0.240..

b) Period:To complete half cycle the time taken is 0.800 sec. To complete one cycle it will take 1.6 sec.

Period is the time to complete one cycle. Here Period is 1.6 sec.

c)Frequency:frequency=1/T where T is the period or time period.

Therefore Frequency=1/1.6 cycles/sec. Here we must denote it in hertz. so frquecy is 1/1.6 hertz