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Physics NEET MCQ
Motion In Two And Three Dimensions Mcq
Quiz 6
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Q.1
A river is flowing from west to east at a speed of 5m/min. A man on the south bank of the river, capable of swimming at 10 m/min in still water, wants to swim across the river in shortest time. He should swim in a direction
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a)due north
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b) 30° east of north
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c)30° west of north
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d)60° east of north
Explanation
Answer: (a)
Q.2
A particle is moving eastwards with velocity of 5m/sec. In 10 sec the velocity changes to 5m/sec north-wards. the average acceleration in this time is [ CPMT 1998]
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a) zero
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b) (1/√2) m/sec2 towards north-west
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c)30° west of north
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d)60° east of north
Explanation
Answer: (b)
Q.3
The magnitude of a given vectors with end points (4, - 4, 0) and (-2, - 2, 0) must be
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a) 6
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b) 5√2
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c)4
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d)2√10
Explanation
Answer:(d)
Q.4
Choose the wrong statement
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a) Three vectors of different magnitudes may be combined to give zero resultant
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b) Two vectors of different magnitudes can be combined to give a zero resultant
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c) The product of a scalar and vector is a vector quantity
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d) All above statements are wrong statement
Explanation
Answer: (b)
Q.5
A boat is sent across a river with velocity of 8km/h. If the resultant velocity of the boat is 10km/h, the river is flowing with velocity of [ CBSE 1994]
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a)12.8 km/hr
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b) 6 km/hr
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c)8 km/hr
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d)10 km/hr
Explanation
Answer: (b)
Q.6
The angle between vectors ( A×B) and (B×A) is
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a) zero
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b) π
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c)π/4
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d)π/2
Explanation
Answer: (b)
Q.7
The vectors 3i - 2j + k and 2i + 6j + ck are perpendicular when
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a) c=6
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b) c=1
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c)c=3
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d)c=8
Explanation
Answer:(a)
Q.8
If two forces are equal and their resultant is also equal to one of them, then angle between the two forces is
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a) 60°
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b) 120°
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c) 90°
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d) 0°
Explanation
Let A be the magnitude of both vectors, given resultant is also A thus A2=A2 + A2 +2A2cosθ cosθ=-1/2 ∴ θ=120° Answer: (b)
Q.9
A boy is hanging from a horizontal branch of tree. The tension in the arms will be maximum when angle between arms is
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a)0°
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b) 30°
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c)60°
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d)120°
Explanation
Answer: (d)
Q.10
Find the value of c is A=0.4i + 0.3j+ck is a unit vector
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a) 0.5
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b) √(0.75)
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c)1
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d)can not be calculated
Explanation
Answer: (b)
Q.11
A bird is flying towards south with velocity 40km/hr and a train is moving with a velocity 40km/hr towards east. What is the velocity of the bird w.r.t. an observer in train
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a) 40√2 km/hr north-east
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b) 40√2 km/hr south-east
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c)40√2 km/hr south-west
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d)40√2 km/hr north-west
Explanation
We want to find velocity of bird with respect to train thus we will reverse vector of velocity of train Answer:(c)
Q.12
The area of a parallelogram formed from the vector A=i + 2j + 3k and B=3i - 2j + k as adjacent sides is
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a) 8√3 units
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b) 64 units
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c) 32 units
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d) √3 units
Explanation
A area of parallelogram with sides as A and B=|A × B|, Now Answer: (a)
Q.13
The resultant of two forces has magnitude 20 Newton. One of the forces is of magnitude 20√3 Newton and makes an angle of 30° with the resultant. Then, the other force must be of magnitude
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a)10N
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b) 20 N
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c)20√3 N
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d)10√3 N
Explanation
Let other vector is of magnitude A and vector of magnitude 20√2 be along x axis then Now if C=A + B then A=C - B Here |C|=20 N and |B|=20√3 N angle between B and C is 30° ∴ A2=C2 + B2 - 2CBcos30 A2=(20)2 + (20√3)2 - 2(20)(20√3)( √3/2) A2=(20)2 + 1200 -1200 A=20 NAnswer: (b)
Q.14
Two forces, one of 10N and other 6N act upon a body. The direction of the forces are unknown, the resultant force on the body is
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a) Not less than 4N and not more than 16N
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b) More than 15N always
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c)More than 6N
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d)More than 10N
Explanation
Answer: (a)
Q.15
The vector sum of N coplanar forces each of magnitude F, when each force is making an angle of 2π/N with the preceding one is
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a) N F
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b)N (F/2)
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c)F/2
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d)zero
Explanation
Answer:(d)
Q.16
A boat moves with speed of 5km/hr relative to water in river flowing with speed of 3 km/hr and having a width of 1km. The time taken around trip is
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a) 5 min
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b) 60 min
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c) 20 min
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d) 30 min
Explanation
Answer: (d)
Q.17
A vector A of magnitude 10 units and another vector of magnitude 6 units are acting at 60° to each other. The magnitude of vector product of two vector is
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a)30 units
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b) 60 unit
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c)30√3 unit
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d)none of the above
Explanation
A × B=ABsinθAnswer: (c)
Q.18
The magnitude of vector can not be
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a) unity
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b) positive
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c)negative
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d)zero
Explanation
Answer: (c)
Q.19
A river is flowing at the rate of 6 km/hr. A swimmer swims across with a velocity of 9 km/hr. The resultant velocity of the man will be in(km/hr)
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a) √(117)
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b) √(340)
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c)√(17)
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d)3√(40)
Explanation
Answer:(a)
Q.20
The area of parallelogram with sides as A=2i + 3j and B=i + 4j
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a) 5 units
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b) 10 units
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c) 15 units
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d) 20 units
Explanation
|A × B|=Area of parallelogram Answer: (a)
Q.21
To a person going east in a car with velocity of 25 km/hr a train appearing to move towards north with velocity of 25√3 km/hr. The actual velocity of the train will be
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a)25 km/hr
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b) 50km/hr
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c)5 km/hr
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d)5√3 km/hr
Explanation
Vector diagram will be Answer: (b)
Q.22
At what angle two forces 2F and √2F acts, so that the resultant force is F√(10) N
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a) 45°
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b) 60°
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c)120°
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d)90°
Explanation
Answer: (a)
Q.23
A stone is dropped from the window of a train moving along a horizontal straight track, the path of the stone as observed by an observer on ground is
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a) straight line
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b) parabolic
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c)circular
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d)hyperbolic
Explanation
Answer:(b)
Q.24
A grasshopper can jump a maximum horizontal distance of 20 cm. If it spends negligible time on the ground, what is its speed of travel along the road
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a) √2 m/s
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b) 1 m/s
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c) (1/√2) m/s
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d) can not be calculated
Explanation
Maximum horizontal range of the grass-hopper=20=u2 /gu=140 cm/shorizontal component of velocity=ucos45=140/√2=100 cm/sec=1m/sec Answer: (b)
Q.25
A particle is projected such that the horizontal range and vertical height are same. Then the angle of projection is
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a)π/4
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b) tan-1(4)
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c)tan-1(1/4)
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d)π/3
Explanation
Answer: (b)
Q.26
The height y and the distance x along the horizontal plane of projectile on a certain planet ( with no surrounding atmosphere) are given by y=(8t-5t2) m and x=6t metre where t is in seconds. The velocity with which the projectile is projected is
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a) 8 m/sec
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b) 6 m/sec
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c) 10 m/sec
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d) not obtainable from the data
Explanation
velocity along x axis=dx/dt=6 m/s velocity along y axis=dy/dt=8 -10t at t=0 Vy=8 m/s Thus velocity at with the projectile is projected Answer: (c)
Q.27
A gun fires two bullets at 60° and 30° with horizontal. The bullets strikes at same horizontal distance. The ratio of maximum height for the two bullets is in the ratio
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a)2:1
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b) 3:1
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c)4:1
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d)1:1
Explanation
Answer: (b)
Q.28
A hose pipe lying on the ground shoots a stream of water upward at an angle of 60° to the horizontal. The speed of the water is 20m/sec as it leaves the hose. It will strike the wall 10 m away at a height of
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a) 10.5 m
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b) 12.32 m
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c)10.0 m
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d)20.0 m
Explanation
θ=60°, u=20 m/s, x=10 m USing equation for trajectoryAnswer: (b)
Q.29
A particle having a mass 0.5 kg is projected under gravity with speed of 98m/s at an angle of 60°. The magnitude of the change of momentum of the particle after 10 seconds is
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a) 0.5 N-sec
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b) 49 N-sec
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c)98 N-sec
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d)490 N-sec
Explanation
Initial velocity along y axis=98sin60=98(√3 /2) Final velocity along y-axis=98(√3 /2) - 9.8× 10 Change in velocity along y axis=98(√3 /2) - 98 - 98(√3 /2) Change in velocity along y-axis=-98 m/s There is no change in velocity along x -axis thus change in momentum=change in momentum along y-axis=(-98)(0.5)=49N-s in magnitude Answer:(b)
Q.30
The range of a particle when launched at an angle of 15° with horizontal is 1.5km. What is the range of the projectile when launched at an angle of 45° to the horizontal.
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a) 1.5 km
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b) 3.0 km
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c) 6.0 km
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d) 0.75 km
Explanation
Use formula for range Answer: (b)
0 h : 0 m : 1 s
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