• Difficult Problems in Physics From post utme (UI 2006)

    Physics

    Chima Sunday (Tutor)
    01-04-2016 15:51:00 +0000

    As rightly said that 'it is not over until its over' Note that the aim of this app is to see you celebrate your MATRICULATION, So in our own way in this room is to review some questions asked in some prominent schools that most people that attempted it failed it.
    About 85% of students that attempted this questions failed it. Try it and see if you can get it right
    Question 1. A simple pendulum makes 50 oscillations in one minute. What is the period of oscillation?
    Option A 0.02s
    Option B 0.20s
    Option C 0.83s
    Option D 1.20s

    Question 2. A girl whose mass is 55kg stands on a spring-weighing machine inside a lift. When the lift starts to ascend, its acceleration is 2ms-2. What will be the reading on the machine? (Take g = 10ms-2 )
    Option A 66kg
    Option B 55kg
    Option C 44kg
    Option D 22kg

    Solutions
    Question 1
    recall that we define period as the time it takes to complete one cycle,
    here 50 oscillation = 60s
    1 oscillation = ?
    cross multiplying, we have that ? = (60s × 1 oscillation)/50 oscillations
    thus ? = 60s/50 = 6s/5 = 1.2s, So correct option is D

    Question 2
    when descending from lift you loos some weight. This apparent loss in weight is dependent on the acceleration at which the lift is descending, thus the reaction
    W = R - F, R = reaction on the foot of tthe girl = mass * gravity = mg. and F = force of the lift = mass * its accleration = ma and W is the weight on the spring
    So W on the spring weighing machine = W = m(g - a) = 55(10 - 2) = 55 * 8 = 440N
    converting Newton to kg we divide by 10, i.e 440/10 = 44kg
    So correct option is C.



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