Work Energy and Power | Physics JEE previous year questions with Solutions

Q 1 :
A force $(3 x^{2} + 2 x - 5) N$ displaces a body from $x = 2 m$ to $x = 4 m .$ Work done by this force is __________ J. [2024]

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(58) $Force, F = (3 x^{2} + 2 x - 5) N, x_{1} = 2 m$ $a n d$ $x_{2} = 4 m$

$Work done, W = \int_{x_{1}}^{x_{2}} F \cdot d x = \int_{2}^{4} (3 x^{2} + 2 x - 5) d x$

$W = {[x^{3}]}_{2}^{4} + {[x^{2}]}_{2}^{4} - 5 {[x]}_{2}^{4} = [64 - 8] + [16 - 4] - 5 [4 - 2] = 58 J$

Q 2 :
A body of mass 50 kg is lifted to a height of 20 m from the ground in the two different ways as shown in the figures. The ratio of work done against the gravity in both the respective cases, will be [2024]

2 : 1
1 : 2
3 : 2
1 : 1

1

2

3

4

(4)

Work done by gravity is path independent, it depends only on vertical displacement, so same work is done in both paths.

Q 3 :
A block is simply released from the top of an inclined plane as shown in the figure above. The maximum compression in the spring when the block hits the spring is [2024]

1 m
$\sqrt{6}$ m
$\sqrt{5}$ m
2 m

1

2

3

4

(4)

$\sin 30 ° = \frac{h}{10} \Rightarrow h = 5$

At maximum compression

using Work-Energy Theorem,

$W_{gravity} + W_{friction} + W_{spring} = Δ K E$

$m g h - μ m g (2 + x) - \frac{1}{2} k x^{2} = 0 - 0$

$5 \times 10 \times 5 - \frac{1}{2} \times 5 \times 10 (2 + x) - \frac{1}{2} 100 \times x^{2} = 0$

$250 - 50 x^{2} - [50 + 25 x] = 0$

$200 - 50 x^{2} - 25 x = 0$

$2 x^{2} + x - 8 = 0$

$x = \frac{- 1 \pm \sqrt{1^{2} + 4 \times 2 \times 8}}{2 \times 2} \Rightarrow x = \frac{- 1 \pm \sqrt{65}}{4} \approx 1.77 m$

Nearest answer is 2m.

Q 4 :
A block of mass 100 kg slides over a distance of 10 m on a horizontal surface. If the coefficient of friction between the surfaces is 0.4, then the work done against friction (in J) is [2024]

4200
3900
4000
4500

1

2

3

4

(3)

Given $m = 100 k g,$ $μ = 0.4$

Friction force, $f = μ m g = 0.4 \times 100 \times 10 = 400 N$

Now $W = f \cdot s = 400 \times 10 = 4000 J$

Q 5 :
A block of mass 1 kg is pushed up a surface inclined to horizontal at an angle of 60 by a force of 10 N parallel to the inclined surface as shown in the figure. When the block is pushed up by 10 m along the inclined surface, the work done against frictional force is $[g = 10 m / s^{2}]$ [2024]

$5 \sqrt{3}$ J
5 J
$5 \times 10^{3}$ J
10 J

1

2

3

4

(2)

$f_{k} = μ_{k} N = μ_{k} m g \cos 60 °$

$f_{k} = 0.1 \times 10 \times \frac{1}{2} = 0.5 N$

$W_{friction} = - f_{k} \cdot S$

$= - (0.5) \times 10$

$W_{friction} = - 5 J$

Topic Question Set

Q 1 :
A force $(3 x^{2} + 2 x - 5) N$ displaces a body from $x = 2 m$ to $x = 4 m .$ Work done by this force is __________ J. [2024]

0%

Q 2 :
A body of mass 50 kg is lifted to a height of 20 m from the ground in the two different ways as shown in the figures. The ratio of work done against the gravity in both the respective cases, will be [2024]

Q 3 :
A block is simply released from the top of an inclined plane as shown in the figure above. The maximum compression in the spring when the block hits the spring is [2024]

Q 4 :
A block of mass 100 kg slides over a distance of 10 m on a horizontal surface. If the coefficient of friction between the surfaces is 0.4, then the work done against friction (in J) is [2024]

Q 5 :
A block of mass 1 kg is pushed up a surface inclined to horizontal at an angle of 60 by a force of 10 N parallel to the inclined surface as shown in the figure. When the block is pushed up by 10 m along the inclined surface, the work done against frictional force is $[g = 10 m / s^{2}]$ [2024]

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Topic Question Set

Q 1 : A force (3x2+2x-5)N displaces a body from x=2m to x=4m. Work done by this force is __________ J. [2024]

0%

Q 2 : A body of mass 50 kg is lifted to a height of 20 m from the ground in the two different ways as shown in the figures. The ratio of work done against the gravity in both the respective cases, will be [2024]

Q 3 : A block is simply released from the top of an inclined plane as shown in the figure above. The maximum compression in the spring when the block hits the spring is [2024]

Q 4 : A block of mass 100 kg slides over a distance of 10 m on a horizontal surface. If the coefficient of friction between the surfaces is 0.4, then the work done against friction (in J) is [2024]

Q 5 : A block of mass 1 kg is pushed up a surface inclined to horizontal at an angle of 60 by a force of 10 N parallel to the inclined surface as shown in the figure. When the block is pushed up by 10 m along the inclined surface, the work done against frictional force is [g=10m/s2] [2024]

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Q 1 :
A force $(3 x^{2} + 2 x - 5) N$ displaces a body from $x = 2 m$ to $x = 4 m .$ Work done by this force is __________ J. [2024]

Q 2 :
A body of mass 50 kg is lifted to a height of 20 m from the ground in the two different ways as shown in the figures. The ratio of work done against the gravity in both the respective cases, will be [2024]

Q 3 :
A block is simply released from the top of an inclined plane as shown in the figure above. The maximum compression in the spring when the block hits the spring is [2024]

Q 4 :
A block of mass 100 kg slides over a distance of 10 m on a horizontal surface. If the coefficient of friction between the surfaces is 0.4, then the work done against friction (in J) is [2024]