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a year ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Four

A fighter plane is flying horizontally at an altitude of 1.5 km with speed 720 km/h. At what angle of sight (w.r.t. horizontal) when the target is seen, should the pilot drop the bomb in order to attack the target?

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alok kumar singh

Contributor-Level 10

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation- when it be at position P, drops a bomb to hit a target T

Let $θ$

Speed of the plane =720km/h = 720 $* 5 / 18$ = 200m/s

Altitude of the plane P'T = 1.5km= 1500m

If bomb hits the target after time t then horizontal distance travelled by the bomb PP'=u $* t$ =200t

Vertical distance travelled by the bomb P'T=1/2gt²

1500 = ½ (9.8)t²

So t²= 1500/4.9, t = $\sqrt[]{\frac{1500}{4.9}} = 17.49 s$

PP'=200 (17.49)m=

tan $θ$ =P'T/P'P=1500/200 (17.49)=0.49287= tan23⁰12'

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New answer posted

a year ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Four

In dealing with motion of projectile in air, we ignore effect of air resistance on motion. This gives trajectory as a parabola as you have studied. What would the trajectory look like if air resistance is included? Sketch such a trajectory and explain why you have drawn it that way.

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alok kumar singh

Contributor-Level 10

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation – due to air resistance particle energy as well as horizontal component of velocity keep on decreasing making the fall steeper then rise. When we are neglecting air resistance path is parabola when we consider air resistance then path is asymmetric parabola.

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a year ago

Physics Physics NCERT Exemplar Solutions Class 11th Chapter Thirteen

Diatomic molecules like hydrogen have energies due to both translational as well as rotational motion. From the equation in kinetic theory pV =2/3 E , E is

(a) The total energy per unit volume

(b) Only the translational part of energy because rotational energy is very small compared to the translational energy

(c) Only the translational part of the energy because during collisions with the wall pressure relates to change in linear momentum

(d) The translational part of the energy because rotational energies of molecules can be of either sign and its average over all the molecules is zero

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Payal Gupta

Contributor-Level 10

This is a multiple choice answer as classified in NCERT Exemplar

(c) According to kinetic theory, we know walls only exert perpendicular forces on molecule. They do not exert parallel force . so there is only change in translational motion.

So pV=2/3E

Where E is representing only translational part of energy.

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a year ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Four

A boy throws a ball in air at 60° to the horizontal along a road with a speed of 10 m/s (36km/h). Another boy sitting in a passing by car observes the ball. Sketch the motion of the ball as observed by the boy in the car, if car has a speed of (18km/h). Give explanation to support your diagram.

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alok kumar singh

Contributor-Level 10

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation – The boy throws the ball at an angle of 60.

Horizontal component of velocity 4cos $?$ = 10cos60

=10 (1/2)

=5m/s.

so horizontal speed of the car is same, hence relative velocity of car and ball in the horizontal direction will be zero.

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New answer posted

a year ago

Physics Physics NCERT Exemplar Solutions Class 11th Chapter Thirteen

ABCDEFGH is a hollow cube made of an insulator (Fig). Face ABCD has positive charge on it. Inside the cube, we have ionized hydrogen. The usual kinetic theory expression for pressure

(a) Will be valid.

(b) Will not be valid since the ions would experience forces other than due to collisions with the walls.

(c) Will not be valid since collisions with walls would not be elastic.

(d) Will not be valid because isotropy is lost.

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Payal Gupta

Contributor-Level 10

This is a multiple choice answer as classified in NCERT Exemplar

(b), (d) due to the presence of external positive charge on face ABCD. The usual expression for pressure on the basis of kinetic energy will not be valid as ions would also experience electrostatic force. So presence of positive charge the isotropy is also lost.

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a year ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Four

A boy travelling in an open car moving on a levelled road with constant speed tosses a ball vertically up in the air and catches it back. Sketch the motion of the ball as observed by a boy standing on the footpath. Give explanation to support your diagram.

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alok kumar singh

Contributor-Level 10

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation – The path of the ball observed by a boy standing on the footpath is parabolic. The horizontal speed of the ball is same as that of the car, therefore ball as well car travels equal horizontal distance, due to vertical speed, the ball follows parabolic path.

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New answer posted

a year ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Four

A, B and C are three non-collinear, non co-planar vectors. What can you say about direction of A * (B * C)?

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alok kumar singh

Contributor-Level 10

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation – the direction of (B $* C$ ) will be perpendicular the plane containing B and B by right hand rule. A $* (B * C)$ will lie in the plane of B and C and is perpendicular to vector A.

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a year ago

Physics Physics NCERT Exemplar Solutions Class 11th Chapter Thirteen

An inflated rubber balloon contains one mole of an ideal gas, has a pressure p, volume V and temperature T. If the temperature rises to 1.1 T, and the volume is increased to 1.05 V, the final pressure will be

(a) 1.1 p

(b) p

(c) Less than p

(d) Between p and 1.1

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Payal Gupta

Contributor-Level 10

This is a multiple choice answer as classified in NCERT Exemplar

(d) pV=nRT

So n= PV/RT

As number moles are fixed

$\frac{P_{1} V_{1}}{{R T}_{1}} = \frac{P_{1} V_{1}}{{R T}_{1}}$

P₂=p₁V₁ (T₂/V₂T₁)

= $\frac{p V ((1.1 T))}{1.05 V ((T))}$

= P $* \frac{1.1}{1.05} \approx 1.05 P$

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New answer posted

a year ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Four

A football is kicked into the air vertically upwards. What is its (a) acceleration, and (b) velocity at the highest point?

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alok kumar singh

Contributor-Level 10

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation- if the football is kicked into the air vertically upwards. Acceleration of football will always vertically downwards and equal to acceleration due to gravity. But when it reaches the highest point its velocity is zero and acceleration is retarding.

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New answer posted

a year ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Four

A ball is thrown from a roof top at an angle of 45° above the horizontal. It hits the ground a few seconds later. At what point during its motion, does the ball have

(a) Greatest speed.

(b) Smallest speed.

(c) Greatest acceleration? Explain

0 Follower 11 Views

alok kumar singh

Contributor-Level 10

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation- at point B it will gain the same speed u and after that speed increases and will be maximum just before reaching point c.

During journey from O to A speed decreases and will be maximum at point A and acceleration is always constant.

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