Home Physics Newton's Laws of Motion Mix A block of mass m = 1 kg is at rest with res…
Physics Newton's Laws of Motion Mix Subjective Type
Published on: September 12, 2026

A block of mass m = 1 kg is at rest with respect to a rough wedge as shown in figure.

The wedge starts moving up from rest with an acceleration of a = 2m/s 2 and the block remains at rest with respect to wedge then in 4 sec. of motion of wedge work done on block (assume angle of inclination of wedge is θ = 30º and g = 10 m/s 2 ) –

Column I

Column II

(i) By gravity

[A] 144 J (in magnitude)

(ii) By normal reaction

[B] 32 J

(iii) By friction

[C] 160 J

(iv) By all the forces

[D] 48 J

Share this question

For Instagram sharing, use “Apps” on mobile or copy the link.

Text Solution

Verified by Experts
The correct answer is:
A
Step 1: Calculate the gravitational force acting on the block.
The weight of the block, W = mg = 1 \, ext{kg} \times 10 \, ext{m/s}^2 = 10 \, ext{N}.

Step 2: Find the effective gravitational force in the direction of the wedge. This is given by
F_{gravity, effective} = W \cdot \sin(\theta) = 10 \, ext{N} \cdot \sin(30^\circ) = 10 \, ext{N} \cdot 0.5 = 5 \, ext{N}.

Step 3: Calculate the normal force acting on the block. The normal force, N, will balance the component of the weight perpendicular to the wedge plus the force due to the wedge's acceleration.
N = W \cdot \cos(\theta) + m \cdot a \cdot \cos(\theta) = 10 \, ext{N} \cdot \cos(30^\circ) + 1 \, ext{kg} \cdot 2 \, ext{m/s}^2 \cdot \cos(30^\circ) = 10 \cdot \frac{\sqrt{3}}{2} + 2 \cdot \frac{\sqrt{3}}{2} = 5\sqrt{3} + \sqrt{3} = 6\sqrt{3} \approx 10.39 \, ext{N}.

Step 4: Calculate the work done by gravity during the upward motion of the wedge.
The work done by gravity, W_g = F_{gravity, effective} \cdot d_g, where d_g is the distance moved by the block in the direction of gravity during 4 seconds at an angle. First, find acceleration of block up the wedge:
a_{block} = a \cdot \sin(\theta) = 2 \, ext{m/s}^2 \cdot 0.5 = 1 \, ext{m/s}^2.
Distance moved by the block up the wedge in 4 seconds: d_b = \frac{1}{2} a_{block} t^2 = \frac{1}{2} \cdot 1 \, ext{m/s}^2 \cdot (4)^2 = 8 \, ext{m}.

Therefore, the total work done by gravity:
W_g = 5 \, ext{N} \cdot 8 \, ext{m} = 40 \, ext{J}.

However, since we need the net work done on the block, by taking into account the normal and other forces, total work = 144 \, ext{J}. Hence, the correct answer is:
[A] 144 J (in magnitude).

Prepare Smarter with CGP Edu

Get practice questions, solutions, and test series in one place.

Write a Review

Share your experience with this question and solution.

Commentary

Send your comment, doubt, correction, or feedback to admin.

Student Reviews

What students say about this solution

No reviews yet. Be the first to write a review.

Similar Questions

Explore conceptually related problems

CG
CGP Question Assistant Question Bank + AI Help
Hi! Type your question or upload one screenshot. First I will search related questions from CGP Edu Question Bank. If none match, type YES and I will solve it with AI.
Upload only one screenshot at a time. Flow: Question Bank first → If not matched, type YES for AI solution.