51.

A boat travels 50 km east, then 120 km North and finally it comes back to the starting point through the shortest distance. The total time of journey is 3 h. What is the average velocity, in km h^-1 over the entire trip ?

• zero

• 100

• 17

• 33.33

A toy cyclist completes one round of a square track of side 2 m in 40 s. What will be the displacement at the end of 3 min ?

• 52 m

• zero

• 16 m

• $2\sqrt{2} \mathrm{m}$

Two trains, each of length 200 m are runmng on parallel tracks. One overtakes the other in 20 s and one crosses the other in 10 s. The velocities of the two trains are

• 5 m/s, 10 m/s

• 10 m/s, 30 m/s

• 15 m/s, 5 m/s

• 20 m/s, 21 m/s

A body starting from rest moves with constant acceleration. The ratio of distance covered by the body during the 5th second to that covered in 5 s is

• $\frac{9}{25}$

• $\frac{3}{5}$

• $\frac{25}{5}$

• $\frac{1}{25}$

The area under acceleration-time graph gives

• distance travelled

• change in acceleration

• force acting

• change in velocity

Two masses M and M/2 are joined together by means of light inextensible string passed over a frictionless pulley as shown in the figure. When the bigger mass is released, the small one will ascend with an acceleration of

• $\frac{\mathrm{g}}{3}$

• $\frac{3\mathrm{g}}{2}$

• $\frac{\mathrm{g}}{2}$

• g

The recoil velocity of a 4.0 kg rifle that shoots a 0.050 kg bullet at a speed of 280 ms^-1 is

• + 3.5 ms^-1

• − 3.5 ms^-1

• $- \sqrt{\left(3.5\right)} {\mathrm{ms}}^{-1}$

• $+ \sqrt{\left(3.5\right)} {\mathrm{ms}}^{-1}$

A man of height h walks in a straight path towards a lamp post of height H with uniform velocity u. Then the velocity of the edge of the shadow on the ground will be

• $\frac{\mathrm{hu}}{\left(\mathrm{H} - \mathrm{h}\right)}$

• $\frac{\mathrm{Hu}}{\left(\mathrm{H} + \mathrm{h}\right)}$

• $\frac{\left(\mathrm{H} - \mathrm{h}\right)}{\mathrm{Hu}}$

• $\frac{\left(\mathrm{H} + \mathrm{h}\right)}{\mathrm{Hu}}$

A train of 150 m length is going towards north direction at a speed of 10 ms^-1. A parrot flies at a speed of 5 ms^-1 towards south direction parallel to the railway track. The time taken by the parrot to cross the train is equal to

• 12 s

• 8 s

• 15 s

• 10 s

An aeroplane is flying horizontally with a velocity of 600 km/h and at a height of 1960 m. When it is vertically above a point A on the ground a bomb is released from it. The bomb strikes the ground at point B. The distance AB is

• 1200 m

• 0.33 km

• 3.33 km

• 33 km