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NEET • PHYSICS • WORK-ENERGY-POWER

Work-energy-power practice · Mixed difficulty

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151 Medium

151 of 347

Understanding +4 | -1

Statement-I: Work done by spring force on a block connected to the spring may be positive or negative.
Statement-II: Spring force is both pushing and pulling.

View answer and explanation

Correct option: A

Statement-I

\&

II are true.

Option A (Statement-I

\& II are true) is correct because the work done by a spring force can be positive or negative depending on the direction of displacement relative to the spring's equilibrium position, and the spring force can indeed be both pushing and pulling.

152 Medium

152 of 347

Understanding +4 | -1

A ball hits the floor and rebounds after inelastic collision. In this case

View answer and explanation

Correct option: C

The total momentum of the ball and the earth is conserved

Option D (The total energy of the ball and the earth is conserved) is correct because, according to the law of conservation of energy, the total energy of an isolated system (ball and Earth) remains constant, although some mechanical energy may be converted to other forms like heat and sound.

153 Medium

153 of 347

Understanding +4 | -1

Statement I In an elastic collision between two bodies, the relative speed of the bodies after collision is equal to the relative speed before the collision. Statement II Inan elastic collision, the linear momentum of the system is conserved.

View answer and explanation

Correct option: B

Statement I is true, Statement II is true; statement II is not correct explanation for statement I

Option B is correct. Statement I is true because the coefficient of restitution is 1 in elastic collisions. Statement II is true because momentum is always conserved in collisions.

154 Easy

154 of 347

Application +4 | -1

A body is moving horizontally at a height of 9 m has its P.E = K.E. Then velocity of that body is

View answer and explanation

Correct option: B

13.5 m/s

Option B (13.5 m/s) is correct because when potential energy equals kinetic energy,

mgh = (1/2)mv^2

, so

v = \sqrt{2gh} = \sqrt{2 * 9.8 * 9} \approx 13.3 m/s

. The closest value is 13.5 m/s.

155 Easy

155 of 347

Application +4 | -1

The kinetic energy of a body varies directly as square of time elapsed. The force acting varies directly as

View answer and explanation

Correct option: D

{t^0}

Option D (

{t^0}

) is correct because if KE varies as

t^2

, then velocity varies as t, and acceleration is constant, making the force constant as well.

156 Medium

156 of 347

Application +4 | -1

A particle of mass m is dropped from rest from a height

{h_0}

on a horizontal floor. The coefficient of restitution between the floor and particle is e. Maximum height attained by the particle after second collision is

View answer and explanation

Correct option: D

{e^4}{h_0}

Option D (

{e^4}{h_0}

) is correct because after two collisions, the height is reduced by a factor of

e^2

each time, resulting in

{e^4}{h_0}

157 Medium

157 of 347

Understanding +4 | -1

Roads are banked on curves so that

View answer and explanation

Correct option: A

The speeding vehicles may not fall outwards

The correct answer is A. Roads are banked on curves to provide the necessary centripetal force to prevent vehicles from skidding outwards.

158 Easy

158 of 347

Application +4 | -1

The energy used by a 100 W bulb which is on for 10 hours is

View answer and explanation

Correct option: D

Both (1) and (2)

Option D (Both (1) and (2)) is correct because 1 kWh and

3.6 \times 10^6 \mathrm{~J}

are equivalent representations of the energy used by the bulb.

159 Medium

159 of 347

Application +4 | -1

A weightless thread can bear tension upto 3.7 kg wt. A stone of mass 500 gms is tied to it and revolved in a circular path of radius 4 m in a vertical plane. If

g = 10\;m{s^{ - 2}}

, then the maximum angular velocity of the stone will be

View answer and explanation

Correct option: A

4 radians/sec

Option A (4 radians/sec) is correct because it is the maximum angular velocity calculated by equating the tension at the lowest point to the maximum tension the string can bear.

160 Medium

160 of 347

Application +4 | -1

A machine which is 75% efficient uses 12 J of energy in lifting up a 1 kg mass through a certain distance. The mass is then allowed to fall through, that distance. The velocity of the ball at the end of its fall is

View answer and explanation

Correct option: C

\sqrt {18} \mathrm{\;m}{\mathrm{s}^{ - 1}}

Option C (

\sqrt {18} \mathrm{\;m}{\mathrm{s}^{ - 1}}

) is correct because 75% of the 12 J energy is converted to potential energy (mgh), which then converts to kinetic energy (1/2 mv²) during the fall. Solving for v gives

\sqrt{18}

m/s.

161 Medium

161 of 347

Analyzing +4 | -1

Statement-I: The workdone in pushing a block is more than the work done in pulling the block on a rough surface.
Statement-II: In the pushing condition normal reaction in more.

View answer and explanation

Correct option: A

Statement-I

\&

II are true.

Option A (Statement-I & II are true) is correct because pushing a block increases the normal reaction, leading to more friction and thus more work done compared to pulling.

162 Medium

162 of 347

Understanding +4 | -1

Identify the wrong statement

View answer and explanation

Correct option: A

A body can have momentum without energy

Option A (A body can have momentum without energy) is the wrong statement because a body with momentum must have kinetic energy, as momentum is directly related to velocity and mass, and kinetic energy is dependent on both.

163 Medium

163 of 347

Application +4 | -1

A car is moving on circular path of radius r = 150 cm its speed is increasing at a rate of

8\,cm/{s^2}

, At some instant of time its speed is 30 cm/s, the net acceleration of the car at this instant is

View answer and explanation

Correct option: B

10\,cm\,{s^{ - 2}}

Option B (

10\,cm\,{s^{ - 2}}

) is correct because it is the net acceleration calculated using both tangential and radial components.

164 Medium

164 of 347

Understanding +4 | -1

For a body in uniform circular motion, the

View answer and explanation

Correct option: C

Angular velocity is constant

Option C (Angular velocity is constant) is correct because, in uniform circular motion, the magnitude of the angular velocity remains constant.

165 Easy

165 of 347

Application +4 | -1

A stone of mass 0.4 kg is attached to a string of length 3 m and is whirled in a horizontal circle. If the string can with stand a tension of 9 N. The maximum velocity with which the stone can be whirled is

View answer and explanation

Correct option: A

8.2 m/s

Option A (8.2 m/s) is correct because the maximum velocity is calculated using the formula

T = mv^2/r

, where T is the tension, m is the mass, v is the velocity, and r is the radius.

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166 Hard

166 of 347

Application +4 | -1

A body is moving unidirectionally under the
influence of a constant power source. Its
displacement in time

t

is proportional to:

View answer and explanation

Correct option: C

{t^{3/2}}

Option C (

{t^{3/2}}

) is correct because the displacement is proportional to time raised to the power of 3/2 when a body moves under constant power.

167 Hard

167 of 347

Application +4 | -1

A mason is supplied with bricks by his assistant who is

3 {~m}

below him, the assistant is tossing the brick vertically up. The speed of the brick, when it reaches the mason is

2 {~ms}^{-1}

. What percentage of energy used up by the servant serves no useful purpose?

View answer and explanation

Correct option: A

5.6

Option C is incorrect. The correct answer is 5.8. The percentage of energy used up by the servant serves no useful purpose is calculated by finding the initial velocity and then calculating the percentage of potential energy converted to kinetic energy.

168 Medium

168 of 347

Application +4 | -1

A spring with spring constant k is extended from

x = 0\;\;\;\mathrm{to\;\;}x = {x_1}

.The work done will be

View answer and explanation

Correct option: B

\frac{1}{2}kx_1^2

Option B (

\frac{1}{2}kx_1^2

) is correct because the work done in extending a spring is equal to the change in its potential energy, which is given by the formula

\frac{1}{2}kx^2

169 Medium

169 of 347

Analyzing +4 | -1

A girl throws a ball with initial velocity

v

at an inclination of

45^{\circ}

. The ball strikes the smooth vertical wall at a horizontal distance

d

from the girl and after rebounding returns to her hand. What is the coefficient of restitution between wall and the ball?

View answer and explanation

Correct option: B

\frac{g d}{v^2-g d}

Option B (

\frac{g d}{v^2-g d}

) is correct because it is derived from analyzing the projectile motion and applying the coefficient of restitution.

170 Medium

170 of 347

Understanding +4 | -1

Two moving particles collide and stick together on a smooth horizontal surface. The following statements are given below

(a) Mechanical energy is conserved.

(b) Total energy is conserved.

(c) Work done by the system is positive

(d) Work done by the system is negative.

Choose the correct option.

View answer and explanation

Correct option: D

(b) and (d) are correct.

Option D ((b) and (d) are correct) is correct because in an inelastic collision where objects stick together, total energy is conserved, but mechanical energy is not, and the work done by the system is negative.

171 Medium

171 of 347

Understanding +4 | -1

A car moves on a circular road. It describes equal angles about the centre is equal intervals of time. Which of the following statements about the velocity of the car is true?

View answer and explanation

Correct option: D

Magnitude to velocity is constant but direction changes

Option D (Magnitude to velocity is constant but direction changes) is correct because the car describes equal angles in equal times (constant speed), but its direction is always changing as it moves along the circular path.

172 Medium

172 of 347

Analyzing +4 | -1

A boy is hanging from a horizontal branch of a tree. The tension in the arms will be maximum when the angle between the arms is

View answer and explanation

Correct option: D

{120^0}

Option D (

{120^0}

) is correct because the tension in the arms is maximized when the angle is largest, as the vertical components of the tension must balance the boy's weight.

173 Medium

173 of 347

Understanding +4 | -1

The kinetic energy acquired by a body of mass m in travelling some distance s, starting from rest under the action of a constant force, is directly proportional to

View answer and explanation

Correct option: A

m^\circ

Option A (

m^\circ

) is correct because the kinetic energy acquired is independent of mass when force and distance are constant, as it depends on work done.

174 Medium

174 of 347

Analyzing +4 | -1

A car when passes through a convex bridge exerts a force on it which is equal to

View answer and explanation

Correct option: D

None of these

Option D (None of these) is correct because the force exerted on the bridge is

Mg - \frac{{M{v^2}}}{r}

, which is not listed in the options.

175 Easy

175 of 347

Application +4 | -1

How much water a pump of 3 kw can raise in one minute to a height of 9 m?

\left( {\mathrm{Take}\,g = 10\,\,m/{s^2}} \right)

View answer and explanation

Correct option: D

2000 litres

The correct answer is D (2000 litres) because the pump's power is used to raise the water's potential energy.

176 Medium

176 of 347

Analyzing +4 | -1

Statement I Two particles moving in the same direction do not lose all their energy in a completely inelastic collision. Statement II Principle of conservation of momentum holds true for all kinds of collisions.

View answer and explanation

Correct option: D

Statement I is true, Statement II is false.

Option C (Statement I is false, Statement II is true) is correct because particles can lose all their energy in a completely inelastic collision if they have equal and opposite momenta, and the principle of conservation of momentum always holds.

177 Medium

177 of 347

Application +4 | -1

Power applied to a particle varies with time t as

P = 4{t^2} - 3t + 2\,watt

, where t is in second. Find the change in its kinetic energy between time t = 0 s and t= 2 s

View answer and explanation

Correct option: B

\frac{{26}}{3}\,J

The correct answer is B (

\frac{{26}}{3}\,J

) because the change in kinetic energy is the integral of power with respect to time.

178 Medium

178 of 347

Understanding +4 | -1

Which of the following statement(s) is/are correct?

I. Spring force is a conservative force.

II. Potential energy is defined only for conservative forces.

View answer and explanation

Correct option: C

Both I and II

The correct answer is C (Both I and II) because spring force is a conservative force, and potential energy is defined only for conservative forces.

179 Medium

179 of 347

Analyzing +4 | -1

Statement-I: If both the speed of a body and radius of its circular path are doubled, then centripetal force also gets doubled.
Statement-II: Centripetal force is directly proportional to both speed of a body and radius of circular path.

View answer and explanation

Correct option: B

Statement-I is true, statement-II is false

Option B (Statement-I is true, statement-II is false) is correct because centripetal force is proportional to the square of the speed and inversely proportional to the radius.

180 Hard

180 of 347

Application +4 | -1

Two bodies having masses 10 kg and 5kg are
moving in concentric orbits of radii 4 and 8 such
that their time periods are the same. Then the ratio
of their centripetal acceleration is:

View answer and explanation

Correct option: A

45689

The question is incomplete and does not provide the correct answer. The ratio of centripetal accelerations should be calculated based on the given masses, radii, and equal time periods. The correct answer should be 2.

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