Motion in a Straight Line Questions and Answers Part-12

1. A body starting from rest moves with constant acceleration. The ratio of distance covered by the body during the 5th sec to that covered in 5 sec is
a) 9/25
b) 3/5
c) 25/9
d) 1/25

Answer: a

2. What determines the nature of the path followed by the particle
a) Speed
b) Velocity
c) Acceleration
d) None of these

Answer: d
Explanation: The nature of the path is decided by the direction of velocity, and the direction of acceleration. The trajectory can be a straight line, circle or a parabola depending on these factors.

3. Two trains, each 50 m long are travelling in opposite direction with velocity 10 m/s and 15 m/s. The time of crossing is
a) 2s
b) 4s
c) \[2\sqrt{3}\] s
d) \[4\sqrt{3}\] s

Answer: b

4. A 120 m long train is moving in a direction with speed 20 m/s. A train B moving with 30 m/s in the opposite direction and 130 m long crosses the first train in a time
a) 6 s
b) 36 s
c) 38 s
d) None of these

Answer: d
Explanation: Total distance = 130 + 120 = 250 m
Relative velocity = 30 -(-20) = 50 m /s
Hence, t = 250 / 50 = 5s

5. A 210 meter long train is moving due North at a of 25m/s. A small bird is flying due South a little above the train with speed 5m/s. The time taken by the bird to cross the train is
a) 6s
b) 7s
c) 9s
d) 10s

Answer: b

6. A police jeep is chasing with, velocity of 45 km/h a thief in another jeep moving with velocity 153 km/h. Police fires a bullet with muzzle velocity of 180 m/s. The velocity it will strike the car of the thief is
a) 150 m/s
b) 27 m/s
c) 450 m/s
d) 250 m/s

Answer: a

7. A boat is moving with velocity of \[3\hat{i}+4\hat{j}\]   in river and water is moving with a velocity of \[-3\hat{i}-4\hat{j}\]  with respect to ground. Relative velocity of boat with respect to water is :
a) \[-6\hat{i}-8\hat{j}\]
b) \[6\hat{i}+8\hat{j}\]
c) \[8\hat{i}\]
d) \[6\hat{i}\]

Answer: b

8. The distance between two particles is decreasing at the rate of 6 m/sec. If these particles travel with same speeds and in the same direction, then the separation increase at the rate of 4 m/sec. The particles have speeds as
a) 5 m/sec ; 1 m/sec
b) 4 m/sec ; 1 m/sec
c) 4 m/sec ; 2 m/sec
d) 5 m/sec ; 2 m/sec

Answer: a
Explanation: When two particles moves towards each other then
v1 + v2 = 6    ...(i)
When these particles moves in the same direction then
v1 + v2 = 4    ...(ii)
By solving v1 = 5 and v2 = 1 m / s

9. A boat moves with a speed of 5 km/h relative to water in a river flowing with a speed of 3 km/h and having a width of 1 km. The minimum time taken around a round trip is
a) 5 min
b) 60 min
c) 20 min
d) 30 min

Answer: d

10. For a body moving with relativistic speed, if the velocity is doubled, then
a) Its linear momentum is doubled
b) Its linear momentum will be less than double
c) Its linear momentum will be more than double
d) Its linear momentum remains unchanged

Answer: c