A ball is dropped from  a high-rise platform at t=0 starting from rest. After 6s another ball is thrown downwards from the same platform with a speed v. The two balls meet at t= 18s. What is the value of v? (take g= 10 ms^-2)

• 74 ms^-2

• 55 ms^-1

• 40 ms^-1

• 60 ms^-1

A.

74 ms^-2

A body of mass 3 kg is under a constant force which causes a displacement s in metres in it, given by the relation , where t is in s. Work done by the force in 2 s is:

• 
• 
• 
• 

C.

If a constant force is applied on the object causing a displacement in it, then it is said that work has been done on the body to displace it.
  Work done by the force  = Force x Displacement
or          W = F x s                            ...(i)
But from Newton's 2nd law, we have
  Force  =  Mass x Acceleration
i.e.,       F = ma                                ...(ii)
Hence, from Eqs. (i) and (ii), we get

Hence, Eq (ii) becomes
                
                   
We have given
                   
 

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

• 0.4 m

D.

0.4 m

Force, 

F = μg
Retardation of the block on the belt

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

• v₁ + v₂ / 2

A particle is moving such that its position coordinates (x,y) are (2m, 3m) at time t = 0, (6m, 7m) at time t = 2 sec and (13 m, 14m) at time t= 5 sec. Average velocity vector (v_av) from t = 0 to t = 5 s is,

• 
• 
• 
• 

D.

Average velocity vector,