A block of $$1$$ kg is released from a top of a smooth curve AB, and then it encounters a rough surface BC, coming to rest at C. The work done by friction is: ($$g=10$$ m/s2)

1. $$25$$ J
2. $$50$$ J
3. $$-25$$ J
4. $$-50$$ J

Subtopic: Â Work Energy Theorem |
Â 69%
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The work done by all the forces (external and internal) on a system equals the change in:

 1 total energy 2 kinetic energy 3 potential energy 4 none of these
Subtopic: Â Work Energy Theorem |
Â 73%
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A bullet from a gun is fired on a rectangular wooden block with velocity $$u$$. When bullet travels $$24$$ cm through the block along its length horizontally, velocity of bullet becomes $$u/3$$. Then it further penetrates into the block in the same direction before coming to rest exactly at the other end of the block. The total length of the block is:
1. $$30$$ cm
2. $$27$$ cm
3. $$24$$ cm
4. $$28$$ cm
Subtopic: Â Work Energy Theorem |
Â 67%
From NCERT
NEET - 2023
Hints

A body of mass $$1$$ kg is thrown upwards with a velocity $$20$$ ms-1. It momentarily comes to rest after attaining a height of $$18$$ m. How much energy is lost due to air friction?
(Take $$g=10$$ ms-2)
1. $$20$$ J
2. $$30$$ J
3. $$40$$ J
4. $$10$$ J

Subtopic: Â Work Energy Theorem |
Â 87%
From NCERT
AIPMT - 2009
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A bicyclist comes to a skidding stop in $$10$$ m. During this process, the force on the bicycle due to the road is $$200$$ N is directly opposed to the motion. The work done by the cycle on the road is:
1. $$+2000$$ J
2. $$-200$$ J
3. zero
4. $$-20000$$ J

Subtopic: Â Work done by constant force |
Â 58%
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The work done by gravity on a projectile of mass $$m$$ fired with a speed $$u$$ at an angle $$\theta$$ to the horizontal, until the time of impact is:

 1 zero 2 $$-\frac12mu^2cos^2\theta$$ 3 $$-\frac12mu^2sin^2\theta$$ 4 $$-\frac12mu^2$$
Subtopic: Â Work done by constant force |
Â 59%
From NCERT
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A force of $$100$$ N acts on a block, always acting opposite to its velocity. The block moves from $$x=4$$ m to $$x=10$$ m and then to $$x=6$$ m. The work done by the force is:
1.  $$200$$ J
2.  $$-200$$ J
3.  $$1000$$ J
4.  $$-1000$$ J
Subtopic: Â Work done by constant force |
From NCERT
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A body of mass $$0.5$$ kg travels in a straight line with velocity $$v=ax^{3/2}$$ where $$a=5~\mathrm{m^{-1/2}s^{-1}}$$. The work done by the net force during its displacement from $$x=0$$ m to $$x=2$$ m is:
1. $$15$$ J
2. $$50$$ J
3. $$10$$ J
4. $$100$$ J

Subtopic: Â Work Done by Variable Force |
Â 66%
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In a ballistics demonstration, a police officer fires a bullet of mass $$50.0$$ g with speed $$200$$ m/s on soft plywood of thickness $$2.00$$ cm. The bullet emerges with only $$\text{10%}$$ of its initial kinetic energy. The emergent speed of the bullet is:
1. $$0$$
2. $$53.2$$ m/s
3. $$63.2$$ m/s
4. $$6.32$$ m/s

Subtopic: Â Work Energy Theorem |
Â 66%
From NCERT
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A horizontal force $$F$$ acts on a $$2$$ kg block placed on a smooth horizontal plane. It varies with time $$t$$ as shown in the figure. The block is initially at rest.

The work done by the force until $$t=2$$ s, equals:
1. $$6.25$$ J
2. $$4.5$$ J
3. $$2.25$$ J
4. $$1.5$$ J
Subtopic: Â Work Done by Variable Force |
Â 62%
From NCERT