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- Question
A boy sitting in a train moving with a uniform velocity drops a coin outside. A man standing outside the train will find the trajectory of the coin to be
Options- A. a parabola
- B. a horizontal straight line
- C. a vertical straight line
- D. a circle
- Correct Answer
- a parabola
ExplanationParabola, because when the coin is dropped at a particular point, it has the same velocity as the running train. So, by Newton's first law, it continues its motion horizontally with that velocity. But then, it is also pulled down by earth's gravity continuously. In this situation its horizontal motion gives way to the parabolic motion until it reaches the ground.
- 1. When one enters a dark room after being in bright light one is not able to see anything clearly for a while because
Options- A. the retina of the eye moves forward
- B. the retina of the eye moves backward
- C. the iris is unable to dilate the pupil immediately to be able to see things
- D. the eye has no power of accommodation Discuss
- 2. Hot water is poured simultaneously in four metallic tumblers painted outside with different points. After some time the water will be found to have cooled most in the tumbler painted.
Options- A. rough white
- B. rough black
- C. shining white
- D. shining black Discuss
- 3. A capillary tube is partially dipped vertically in a vessel containing water. Due to capillarity water rises in the tube. The height of water rise in the tube can be increased by
Options- A. decreasing the radius of the capillary tube
- B. increasing the radius of the capillary tube
- C. increasing the height of water in the vessel
- D. None of these Discuss
- 4. The electrical domestic tube light gives white fluorescent light because of
Options- A. colision between molecules of filled gas under electric current
- B. heavy current
- C. vacuum inside the tube
- D. falling of ultra violet rays on the white inner coating of the tube Discuss
- 5. Pick out the only vector quantity
Options- A. pressure
- B. impulse
- C. gravitational potential
- D. co-efficient of friction Discuss
- 6. In the case of bodies falling under gravity which of the following remains constant at a given place?
Options- A. Kinetic energy
- B. Potential energy
- C. acceleration
- D. all the above Discuss
- 7. A boy is swinging a ball attached to a string in a horizontal circle.If the string snaps
Options- A. the ball will travel towards the center of the circle and fall down
- B. it will continue to travel along a tangent to the circle at the point the ball was at the time of snapping and finally fall down
- C. it will fall down at the same place where the string breaks
- D. none of these Discuss
- 8. In case of uniform circular motion, the acceleration is
Options- A. Variable in magnitude but constant in direction
- B. Constant in magnitude and directed radially inwards
- C. Variable in magnitude but tangential to the circle
- D. Zero Discuss
- 9. What is refractive index ?
Options- A. it is defined as the ratio of speed of light in the medium to the speed of light in vacuum.
- B. it is defined as the product of speed of light in medium and in vacuum.
- C. it is defined as the ratio of speed of light in vacuum to the speed of light in the medium .
- D. None of above Discuss
- 10. A hunter on the ground wishes to shoot a bird on a tree at a distance with his rifle. He has to point the rifle
Options- A. at the lower alevation than the bird
- B. at a higher alevation than the bird
- C. In the same direction as the bird
- D. vertically upwards Discuss
Physics problems
Search Results
Correct Answer: the iris is unable to dilate the pupil immediately to be able to see things
Explanation:
The size of the pupil of the automatically adjusts itself according to the intensity of light passing through it; if the intensity is more, the size is less, if less, it is more. So in our case the pupil should dilate i.e , increase in size to be able to see in the dark. This switchover takes some time. But here the entry into the dark room is immediate. So the eye has no time to adjust itself and hence is not able to see at all for a while.
Correct Answer: rough black
Explanation:
Black surfaces are good emitters of heat ( They are also good absorbers of heat). If the black surface is rough too, the emitting will be better. So (b) is the correct answer. Shining surfaces reflect back radiation. So if the black surface is also shining the effectiveness of emitting heat is lessened.
Correct Answer: decreasing the radius of the capillary tube
Explanation:
The water rise in a capillary tube dipped in water is such that the weight of water in the tube above the surface of water in the vessel is equal to (balances) the upward force due to surface tension. So it is clear that if the the bore (radius) to the tube is decreased, the height of the water column in it must be greater. So, (a) is correct.
Correct Answer: falling of ultra violet rays on the white inner coating of the tube
Explanation:
The ultraviolet rays have high frequency and shorter wavelength are converted to visible white light with lower frequency and greater wave length
Correct Answer: impulse
Correct Answer: acceleration
Explanation:
This acceleeration denoted by letter g varies from place to place. Unless stated otherwise, it can be taken 9.8 m/ .
Correct Answer: it will continue to travel along a tangent to the circle at the point the ball was at the time of snapping and finally fall down
Explanation:
The centripetal force having been removed the body cannot execute the curved path. (B) is Correct.
Correct Answer: Variable in magnitude but constant in direction
Correct Answer: it is defined as the ratio of speed of light in vacuum to the speed of light in the medium .
Correct Answer: at a higher alevation than the bird
Explanation:
The trajectory of the bullet is a parabola
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