CBSE Class – XI Physics (Set 3) Last year Paper (2015-16)

Time: 3 Hrs. M.M: 70

General Instructions:

Question 1 to 5 one mark.

1. Question 6 to 10 each two mark.
2. Question 11 to 22 each three mark.
3. Question 23 is value based question and carry four marks.
4. Questions 24 to 26 each five mark.

Section A

1. Find the dimensional formula for coefficient of viscosity (<math>\eta</math>).

Write properties of an ideal fluid.

1. If pressure is made 16 times, what will be the effect on the velocity of sound?
2. Given that for two vectors A and B, <math>|A \times B| = |AB|</math>. Find the acute angle between A and B.
3. A body of mass m is oscillating harmonically suspended from a mass less spring of spring constant k. What is the time period?

Section B

1. If <math>a = 2\hat{i} + 3\hat{j} - 4\hat{k}</math> and <math>b = 4\hat{i} + 3\hat{j} - 2\hat{k}</math>. Find the angle between a and b.

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Establish the given vector inequality geometrically or otherwise <math>|a+b| < |a| + |b|</math> When does the equality sign above apply?

From the properties of a triangle, one side of a triangle is always less than the sum of the lengths of its two other sides.

1. Define inertial and non-inertial frame of references. What is pseudo force?
2. Solve the expression for potential energy of a spring when elongation in the spring is x.

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9. Write expression for work done in blowing a soap bubble from radius <math>r_1</math> to <math>r_2</math>. Calculate it to increase radius from r to 2r.

1. A Carnot's engine has the same efficiency
2. between 500 K and 100 K
3. between 1000 K and T K

Find the value of T.

Section C

1. (i) Using the relation E = hv, obtain the dimensions of Planck constant.
2. The resistance R is given by relation

R = V/I. If potential difference V is <math>100 \pm 5V</math> and current I is <math>10 \pm 0.2</math> A. Calculate the percentage error in R.

1. A car accelerates from rest to a constant rate a for some time, after which it decelerates at a constant rate p to come to rest. If t is the total time elapsed, then calculate
2. the maximum velocity attained by the car.
3. the total distance travelled by the car.
4. A projectile is fired horizontally from the top of a tower. Find the expression for its time of descent and horizontal range.
5. Distinguish between static friction, limiting friction and kinetic friction. How do they vary with the applied force, explain by diagram.

1. Two pendulums with identical bobs and lengths are suspended from a common support

such that in rest position the two bobs are in contact as shown in figure alongside. One of the bobs is released after being displaced by 10° so that it collides elastically head-on with the other bob.

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1. Describe the motion of two bobs.
2. Draw a graph showing variation in energy of either pendulum with time, for <math>0 \le t \le 2t</math>, where T is the time period of each pendulum.

1. (n-1) equal point masses each of mass m are placed at the vertices of a regular n polygon.

The vacant vertex has a position vector a with respect to the centre of the polygon. Find the position vector of centre of mass. 2/5