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• # Common Questions Ask in Post UTME Physics Exam Day7

Physics

Chima Sunday (Tutor)
23-06-2016 17:30:00 +0000

Try your best to solve these questions. Show working on paper when necessary and include a picture of your hand written Solution in your response. Wish you the best!

1. A body of density 0.8kgm-3 weighs 120N in air. It is suspended with a string with half of its volume immersed in a liquid of density 0.6kg/m-3. Find the tension in the string
A. 75N
B. 65N
C. 45N
D. 35N
(uniben)

Updated Solution
Note all quantity is in its SI unit
density of body = 0.8; weight in air = 120; recall that weight = mg
So m = weight/g = 120/10 = 12
recall that density = m/V; V = m/density = 12/0.8 = 15
If the half of the volume is immersed in water, it therefore follows immediately from Archimedes that the volume of water displaced is half of the volume, so the mass of liquid displace is given thus, m = V × density = 15/2 × 0.6 = 4.5
thus weight of liquid displace = 4.5 × 10 = 45 = Upthrust U
from principle of flotation, U = Weight in air - Weight in liquid
45 = 120 - Weight in liquid
Weight in liquid = 120 - 45 = 75
So Answer is Option A

2. Some quantity of hot water at a temperature T is added to warm water at a temperature of 25oc in the ratio 1:4. Determine T if the final temperature of the mixture is 30oc
A. 35oc
B. 30oc
C 50oc D. 55oc
E. 10oc
(futo)

Updated Solution
Heat lost quantity of water m = mc(T - 30)
Heat gain by quantity of water M = Mc(30 - 25)
neglecting heat loss to the environment, so mc(T - 30) = Mc(30 - 25)
m(T - 30) = M(5)
from question ratio of quantity is 1:4, so m/M = 1/4 and M/m = 4
thus T - 30 = M/m(5) = 4 × 5 = 20
T = 20 + 30 = 50
Answer is Option C

3. A uniform rod 10m long is balanced on a pivot placed at its midpoint, a girl of mass 30kg sits on arm of the rod at a point 3m away from the pivot. What mass can be place 2m away from the other end of the rod to keep the rod horizontal?
A. 30kg
B. 45kg
C. 20kg
D. 40kg
(abu)

Updated Solution
From principle of moment, ACM = CWM
So taking moment at the pivot
30 × 3 = m(5 - 2)
90 = 3m
m = 30
In fact we can even guess the answer rightly, without actually solving it, if you really understand the physical interpretation of principle of moment.
So the correct answer is A

• Oluwamuyiwa O.T

1.A 2.C 3.A

5 23-06-2016 17:42:00 +0000

• armsy mohd

1, B 2. D 3. D

5 24-06-2016 10:45:00 +0000

• Damian Nonsy

1. C 2. no sure 3. D

5 24-06-2016 12:22:00 +0000

• Oluwamuyiwa O.T

1.C

5 24-06-2016 15:52:00 +0000

• Oluwamuyiwa O.T

5 24-06-2016 16:07:00 +0000

• Oluwamuyiwa O.T

5 24-06-2016 16:24:00 +0000

• Oluwamuyiwa O.T

5 24-06-2016 16:29:00 +0000

• Chima Sunday (Tutor)

Thumb up to Arms, Damian and Otun for that wonderful and fearless attempt, really appreciate you guys effort, please keep it up and lets keep this fire burning and illuminating every dark corner of your knowledge. Please do note that this post has been updated, with solution, please try and check it. Do feel free to ask your questions. Wish you more than best. Cheers!

5 27-06-2016 11:20:00 +0000

• Musa Sabiu Ibrahim

Wow good

5 28-01-2017 22:27:00 +0000