# A man pushes a wall and fails to displace it. He does: 1. negative work 2. positive but not maximum work 3. no work at all 4. maximum work

Subtopic:  Concept of Work |
87%
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PMT - 1992
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The minimum work done in pulling up a block of wood weighing $$2$$ kN for a length of $$10$$ m on a smooth plane inclined at an angle of $$15^\circ$$ with the horizontal is (given: $$\mathrm{sin}15^\circ=0.2588)$$:
1. $$4.36$$ kJ
2. $$5.17$$ kJ
3. $$8.91$$ kJ
4. $$9.82$$ kJ

Subtopic:  Work done by constant force |
79%
From NCERT
PMT - 2003
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A spherical ball of mass 20 kg is stationary at the top of a hill of height 100 m. It slides down a smooth surface to the ground, then climbs up another hill of height 30 m and finally slides down to a horizontal base at a height of 20 m above the ground. The velocity attained by the ball is:

 1 $$10 \mathrm{~m} / \mathrm{s}$$ 2 $$10 \sqrt{30} \mathrm{~m} / \mathrm{s}$$ 3 $$40 \mathrm{~m} / \mathrm{s}$$ 4 $$20 \mathrm{~m} / \mathrm{s}$$
Subtopic:  Conservation of Mechanical Energy |
61%
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A quarter horse-power motor runs at a speed of 600 rpm. Assuming 40% efficiency, the work done by the motor in one rotation will be:

1. 7.46 J

2. 7400 J

3. 7.46 ergs

4. 74.6 J

Subtopic:  Power |
54%
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Two equal masses, $$m_1$$ and $$m_2,$$ moving in the same straight line at velocities +3 m/s and –5 m/s respectively, collide elastically. Their velocities after the collision will be:

1. +4 m/s for both

2. –3 m/s and +5 m/s

3. –4 m/s and +4 m/s

4. –5 m/s and +3 m/s

Subtopic:  Collisions |
81%
From NCERT
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A uniform chain of length $$L$$ and mass $$M$$ is lying on a smooth table and one-third of its length is hanging vertically down over the edge of the table. If $$g$$ is acceleration due to gravity, the work required to pull the hanging part on the table is:

1. $$MgL$$

2. $$MgL/3$$

3. $$MgL/9$$

4. $$MgL/18$$

Subtopic:  Gravitational Potential Energy |
72%
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A particle of mass 'm' is moving in a horizontal circle of radius 'r' under a centripetal force equal to –K/r2, where K is a constant. The total energy of the particle will be:

1. $\frac{K}{2r}$

2. $-\frac{K}{2r}$

3. $-\frac{K}{r}$

4. $\frac{K}{r}$

Subtopic:  Potential Energy: Relation with Force |
58%
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A force $\mathbit{F}=-k\left(y\mathbit{i}+x\mathbit{j}\right)$ (where k is a positive constant) acts on a particle moving in the xy-plane. Starting from the origin, the particle is taken along the positive x-axis to the point (a, 0) and then parallel to the y-axis to the point (a, a). The total work done by the force on the particle is:

1. $-2k{a}^{2}$

2. $2k{a}^{2}$

3. $-k{a}^{2}$

4. $$ka^2$$

Subtopic:  Work Done by Variable Force |
56%
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A lorry and a car moving with the same K.E. are brought to rest by applying the same retarding force, then:

1. Lorry will come to rest in a shorter distance

2. Car will come to rest in a shorter distance

3. Both will come to rest in a same distance

4. None of the above

Subtopic:  Work Energy Theorem |
64%
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The relationship between force and position is shown in the given figure (in a one-dimensional case). The work done by the force in displacing a body from $$x = 1$$ cm to $$x = 5$$ cm is:

1. $$20$$ ergs
2. $$60$$ ergs
3. $$70$$ ergs
4. $$700$$ ergs

Subtopic:  Work Done by Variable Force |
83%
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