Two trains, each 50 m long, are travelling in the opposite direction with velocities 10 m/s and 15 m/s. The time of crossing is:

1. 10 sec

2. 4 sec

3. $2\sqrt{3}$ $\sec$

4. $4\sqrt{3}$ $\sec$

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  

1.  4 s
2.  36 s
3.  38 s
4.  5 s

A 210-meter long train is moving due north at a speed of 25 m/s. A small bird is flying due South a little above the train with a speed of 5m/s. The time taken by the bird to cross the train is 

(1) 6 s

(2) 7 s

(3) 9 s

(4) 10 s

A police jeep is chasing with a velocity of 45 km/h a thief in another jeep moving with a velocity of 153 km/h. Police fire a bullet with a muzzle velocity of 180 m/s. The velocity with which it will strike the car of the thief is 

1.  150 m/s
2.  27 m/s
3.  450 m/s
4.  250 m/s

A train of 150 meter length is going towards north direction at a speed of 10 m/sec. A parrot flies at the speed of 5 m/sec towards south direction parallel to the railway track. The time taken by the parrot to cross the train is 

(1) 12 sec

(2) 8 sec

(3) 15 sec

(4) 10 sec

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: 

(1) $-6\hat{i}-8\hat{j}$

(2) $6\hat{i}+8\hat{j}$

(3) $8\hat{j}$

(4) $6\hat{i}$

The distance between two particles is decreasing at the rate of 6 m/sec when they are moving in the opposite directions. If these particles travel with the same initial speeds and in the same direction, then the separation increases at the rate of 4 m/sec. It can be concluded that particles' speeds could be

1. 5 m/sec, 1 m/sec

2. 4 m/sec, 1 m/sec

3. 4 m/sec, 2 m/sec

4. 5 m/sec, 2 m/sec

An express train is moving with a velocity v₁. Its driver finds another train is moving on the same track in the same direction with velocity v₂. To escape collision, driver applies a retardation 'a' on the train. The minimum time of escaping collision will be 

1.  $t=\frac{v_1-v_2}{a}$
2.  $t_1=\frac{v_1^2-v_2^2}{2}$
3.  None
4.  Both

A stone falls from a balloon that is descending at a uniform rate of 12 m/s. The displacement of the stone from the point of release after 10 sec is

(1) 490 m

(2) 510 m

(3) 610 m

(4) 725 m

A ball is dropped on the floor from a height of 10 m. It rebounds to a height of 2.5 m. If the ball is in contact with the floor for 0.01 sec, the average acceleration during contact is 

1. 2100 m/sec² downwards

2. 2100 m/sec² upwards

3. 1400 m/sec²

4. 700 m/sec²