A particle covers half of its total distance with speed v₁ and the rest half distance with speed v₂. Its average speed during the complete journey is

• v₁v₂ / v₁ + v₂

• 2v₁v₂/v₁ + v₂

• 2v₁²v²₂ / v₁² + v²₂

• 2v₁²v²₂ / v₁² + v²₂

A plank with a box on it at one end is gradually raised about the other end. As the angle of inclination with the horizontal reaches 30^o, the box starts to slip and slides 4.0 m down the plank in 4.0 s. The coefficients of static and kinetic friction between the box and the plank will be respectively

• 0.6 and 0.6

• 06 and 0.5

• 0.5 and 0.6 

• 0.4 and 0.3

A conveyor belt is moving at a constant speed of 2 m/s. A box is gently dropped on it. The coefficient of friction between them is μ = 0.5. The distance that the box - will move relative to belt before coming to rest on it taking 
g= 10 ms^{-2 is}

• 1.2 m

• 0.6 m

• zero

• zero

Three blocks will masses m, 2m and 3m are connected by strings, as shown in the figure. After an upward force F is applied on block m, the masses move upward at constant speed v. What is the net force on the block of mass 2m? (g is the acceleration due to gravity)

• zero

• 2 mg

• 3 mg

• 3 mg

A uniform force of (3 i + j) N acts on a particle of mass 2 kg. Hence the particle is displaced from position (2 i + k) m to position ( 4 i + 3 j - k) m. The work done by the force on the particle is,

• 9 J

• 6 J

• 13 J

• 13 J