## 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

Explanation:

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

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

Explanation:

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

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

Explanation:

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

Explanation:

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) $6\hat{i}$

Explanation:

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

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