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A body of mass 5text kg moving with a uniform speed 3sqrt2text ms^-1 in X–Y plane along the line y = x + 4. The angular momentum of the particle about the origin will be ______ textkg m^2texts^-1.

Numerical Answer Type:
Enter a numerical value Answer: 60 to 60 +4 marks

Solution & Explanation

### Related Formula The magnitude of the angular momentum L of a particle of mass m moving with velocity v is: L = m v d where: * d is the perpendicular distance from the axis of rotation (origin) to the line of motion of the particle. ### Core Logic Given parameters: * Mass, m = 5text kg * Velocity, v = 3sqrt2text ms^-1 * Line of motion: y = x + 4 implies x - y + 4 = 0 ### Step 1: Calculate Perpendicular Distance The perpendicular distance d from the origin (0,0) to the line Ax + By + C = 0 is: d = frac|A(0) + B(0) + C|sqrtA^2 + B^2 For the line x - y + 4 = 0: d = frac|4|sqrt1^2 + (-1)^2 = frac4sqrt2 = 2sqrt2text m ### Step 2: Calculate Angular Momentum Substitute the values into the angular momentum formula: L = m v d L = 5text kg times (3sqrt2text ms^-1) times (2sqrt2text m) L = 5 times 3 times 4 = 60text kg m^2texts^-1 Thus, the angular momentum of the particle about the origin is 60text kg m^2texts^-1. ### Pattern Recognition Instead of complicated vector cross products, find the perpendicular distance of the straight line from the origin using standard coordinate geometry. L = mvd is extremely fast and reliable. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Physics: System of Particles and Rotational Motion

More System of Particles and Rotational Motion Previous-Year Questions — Page 8

Q55 jee_main_2024_31_jan_evening Angular Momentum
A body of mass 'm' is projected with a speed 'u' making an angle of 45^circ with the ground. The angular momentum of the body about the point of projection, at the highest point is expressed as fracsqrt2 m u^3X g. The value of 'X' is ________.
Numerical Answer. Answer: 8 to 8

Solution

### Related Formula H = fracu^2 sin^2 theta2g L = m v_x H_max (for highest point) ### Core Logic At the highest point in a projectile's trajectory, the velocity is entirely horizontal (v_x = u cos theta). The perpendicular distance from the point of projection to the line of motion is the maximum height H. ### Step 1: Calculate Velocity and Height Horizontal velocity: v_x = u cos theta Maximum height: H = fracu^2 sin^2 theta2g ### Step 2: Angular Momentum Calculation L = m times (u cos theta) times left(fracu^2 sin^2 theta2gright) For theta = 45^circ: cos(45^circ) = 1/sqrt2 sin^2(45^circ) = (1/sqrt2)^2 = 1/2 L = m times left(fracusqrt2right) times left(fracu^2 (1/2)2gright) L = m times fracusqrt2 times fracu^24g = fracm u^34sqrt2 g ### Step 3: Match Format We need the format to be fracsqrt2 m u^3X g. Multiply numerator and denominator by sqrt2: L = fracsqrt2 m u^34 times 2 times g = fracsqrt2 m u^38g Thus, X = 8. ### Pattern Recognition Angular momentum at the apex is always m(u costheta)(H_max). Be careful with algebraic rationalization at the end to match the given exact format. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Physics: System of Particles and Rotational Motion Class 11 Physics: Motion in a Plane
Q58 jee_main_2024_31_jan_evening Moment of Inertia
Two identical spheres each of mass 2 text kg and radius 50 text cm are fixed at the ends of a light rod so that the separation between the centers is 150 text cm. Then, moment of inertia of the system about an axis perpendicular to the rod and passing through its middle point is fracx20 text kg m^2, where the value of x is
Numerical Answer. Answer: 53 to 53

Solution

### Related Formula I = I_cm + Md^2 For a solid sphere, I_cm = frac25MR^2. ### Core Logic Apply the Parallel Axis Theorem for each sphere. The total moment of inertia is twice the moment of inertia of a single sphere shifted from its center to the middle of the rod.
Moment of Inertia diagram for Q58 - JEE Main 2024 Evening
Moment of Inertia diagram for Q58 - JEE Main 2024 Evening
### Step 1: Establish Parameters Mass M = 2 text kg Radius R = 50 text cm = 0.5 text m = frac12 text m Distance between centers = 150 text cm = 1.5 text m. Distance from axis of rotation to the center of each sphere is d = frac1.52 = 0.75 text m = frac34 text m. ### Step 2: Calculate Inertia I_total = 2 times left[ frac25MR^2 + Md^2 right] I_total = 2 times left[ frac25(2)left(frac12right)^2 + (2)left(frac34right)^2 right] I_total = 2 times left[ frac45left(frac14right) + 2left(frac916right) right] I_total = 2 times left[ frac15 + frac98 right] I_total = 2 times left[ frac8 + 4540 right] I_total = 2 times frac5340 = frac5320 text kg m^2 ### Step 3: Extract x Comparing with fracx20 text kg m^2, we get: x = 53 ### Pattern Recognition Watch out for units. Convert cm to meters immediately. Use fractions (1/2 and 3/4) instead of decimals to rapidly solve the resulting squared terms without arithmetic errors. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Physics: System of Particles and Rotational Motion
Q54 jee_main_2024_31_jan_morning Rolling Kinetic Energy
A solid circular disc of mass 50 mathrm~kg rolls along a horizontal floor so that its center of mass has a speed of 0.4 mathrm~m / mathrms. The absolute value of work done on the disc to stop it is ______ mathrmJ.
Numerical Answer. Answer: 6 to 6

Solution

### Related Formula W = Delta textKE K_textrolling = frac12 m v^2 left(1 + frack^2R^2right) ### Core Logic According to the Work-Energy Theorem, the total work done is equal to the change in kinetic energy. Since the disc comes to rest, final kinetic energy is zero. W = 0 - left(frac12 m v^2 + frac12 I omega^2right) ### Step 2: Calculation For a solid circular disc, I = frac12mR^2, thus frack^2R^2 = frac12. W = - frac12 m v^2 left(1 + frack^2R^2right) W = - frac12 times 50 times (0.4)^2 left(1 + frac12right) W = - 25 times 0.16 times 1.5 W = - 6mathrm\,J The absolute value of work done |W| = 6mathrm\,J. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Physics: System Of Particles And Rotational Motion Class 11 Physics: Work, Energy And Power

More System of Particles and Rotational Motion Questions — jee_main_2024_29_january_evening

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