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Physics Unit Test: Work, Power & Energy(June 25) - JEE MCQ


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15 Questions MCQ Test Daily Test for JEE Preparation - Physics Unit Test: Work, Power & Energy(June 25)

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Physics Unit Test: Work, Power & Energy(June 25) - Question 1

A block of mass m attached to a massless spring is performing oscillatory motion of amplitude 'A' on a frictionless horizontal plane. If half of the mass of the block breaks off when it is passing through its equilibrium point, the amplitude of oscillation for the remaining system become fA. The value of f is

Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 1

Physics Unit Test: Work, Power & Energy(June 25) - Question 2

A 60 HP electric motor lifts an elevator having a maximum total load capacity of 2000 kg. If the frictional force on the elevator is 4000 N, the speed of the elevator at full load is close to: (1 HP = 746 W, g = 10 ms-2)

Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 2

Ftotal = Mg + friction
= 2000 × 10 + 4000
= 20,000 + 4000 = 24,000 N
P = F × v
60 × 746 = 24,000 × v
⇒ v = 1.86 m/s  1.9 m/s

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*Answer can only contain numeric values
Physics Unit Test: Work, Power & Energy(June 25) - Question 3

In a spring gun having spring constant 100 N/m, a small ball 'B' of mass 100 g is put in its barrel (as shown in figure) by compressing the spring through 0.05 m. There should be a box placed at a distance 'd' on the ground so that the ball falls in it. If the ball leaves the gun horizontally at a height of 2 m above the ground, the value of d is _______________ m.
(g = 10 m/s2) (in integers)


Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 3




kx2 = mv2


From h = gt2

d = vt = 0.5

Physics Unit Test: Work, Power & Energy(June 25) - Question 4

A body at rest is moved along a horizontal straight line by a machine delivering a constant power. The distance moved by the body in time 't' is proportional to

Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 4

Physics Unit Test: Work, Power & Energy(June 25) - Question 5

Given below is the plot of a potential energy function U(x) for a system, in which a particle is in one dimensional motion, while a conservative force F(x) acts on it. Suppose that Emech = 8 J, the incorrect statement for this system is:

Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 5

Emech. = 8 J
(A) At x > x4, U = constant = 6 J
K = Emech. - U = 2 J = constant

(B) At x < x1, U = constant = 8 J
K = Emech - U = 8 - 8 = 0 J
The particle is at rest.

(C) At x = x2, U = 0 ⇒ Emech. = K = 8 J
K.E. is greatest and the particle is moving at fastest speed.

(D) At x = x3, U = 4 J
U + K = 8 J
K = 4 J

*Answer can only contain numeric values
Physics Unit Test: Work, Power & Energy(June 25) - Question 6

A particle of mass 1 kg is hanging from a spring of force constant 100 Nm-1. The mass is pulled slightly downward and released, so that it executes free simple harmonic motion with time period T. The time when the kinetic energy and potential energy of the system will become equal is T/x. The value of x is _______. (in integers)


Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 6

Physics Unit Test: Work, Power & Energy(June 25) - Question 7

A free electron of 2.6 eV energy collides with a H+ ion. This results in the formation of a hydrogen atom in the first excited state and a photon is released. Find the frequency of the emitted photon (h = 6.6 × 10-34 J s).

Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 7

For every large distance, P.E. = 0
Total energy = 2.6 + 0 = 2.6 eV
Finally, in the first excited state of H atom, total energy = -3.4 eV
Loss in total energy = 2.6 - (-3.4) = 6 eV
It is emitted as photon.
= 206 nm
F =  = 1.45 1015 Hz
= 1.45 × 109 MHz

Physics Unit Test: Work, Power & Energy(June 25) - Question 8

A body of mass M at rest explodes into three pieces, in the ratio of masses 1 : 1 : 2. Two smaller pieces fly off perpendicular to each other with velocities of 30 ms-1 and 40 ms-1 respectively. The velocity of the third piece will be:

Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 8

Mass of pieces according to the statement-

According to law of conservation of momentum


As  &  are perpendicular
so 
P3 = (50) 

so v = 25 ms-1

Physics Unit Test: Work, Power & Energy(June 25) - Question 9

A particle of mass 500 gm is moving in a straight line with velocity v = b x5/2. The work done by the net force during its displacement from x = 0 to x = 4 m is: (Take b = 0.25 m-3/2 s-1)

Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 9

From the work energy theorem,
Work done by net force = ΔK.E.
⇒ w = 
w = 1/2× 0.5 × (0.25)2 × (4)5
w = 16 J

Physics Unit Test: Work, Power & Energy(June 25) - Question 10

A body of mass 0.5 kg travels on a straight line path with velocity v = (3x2 + 4) m/s. The net work done by the force during its displacement from x = 0 to x = 2 m is:

Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 10

Given,
Mass = 0.5 kg
At x = 0
vi = 3(02) + 4 = 4
At x = 2
v= 3(2)2 + 4
= 16
W = ΔK = m(162 - 42)
= 1/2 x 1/2 (256 - 16)
= 240/4 = 60 J

Physics Unit Test: Work, Power & Energy(June 25) - Question 11

As per the given figure, two blocks each of mass 250 g are connected to a spring of spring constant 2 Nm-1. If both are given velocity v in opposite directions, then maximum elongation of the spring is:

Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 11



Using energy conservation,

 
 x = v / 2

Physics Unit Test: Work, Power & Energy(June 25) - Question 12

Two cylindrical vessels of equal cross-sectional area 16 cm2 contain water up to heights 100 cm and 150 cm, respectively. The vessels are interconnected so that the water levels in them become equal. The work done by the force of gravity during the process is: [Take density of water = 103 kg/m3 and g = 10 ms-2]

Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 12

*Answer can only contain numeric values
Physics Unit Test: Work, Power & Energy(June 25) - Question 13

A block of mass 'm' (as shown in figure) moving with kinetic energy E compresses a spring through a distance 25 cm when its speed is halved. The value of spring constant of used spring will be nE Nm-1 for n = _____________. (in integers)


Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 13

Physics Unit Test: Work, Power & Energy(June 25) - Question 14

A stone of mass m tied to a string is being whirled in a vertical circle with a uniform speed. The tension in the string is

Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 14



At any θ,
T - mgcosθ = 
⇒ T = mg cosθ 

Since is constant,
⇒ will be minimum when cos θ is minimum.
⇒ θ = 180° corresponds to Tminimum.

Physics Unit Test: Work, Power & Energy(June 25) - Question 15

A particle experiences a variable force in a horizontal x-y plane. Assume distance in meters and force in newton. If the particle moves from point (1, 2) to point (2, 3) in the x-y plane; then kinetic energy changes by

Detailed Solution for Physics Unit Test: Work, Power & Energy(June 25) - Question 15

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