Question

1.When a body is stationary:
a) there is no force acting on it
b) the forces acting on it are not in contact with it
c) the combination of forces acting on it balance each other
d) the body is in vacuum.

2) A particle is moving with a constant speed along a straight line path. A force is not required to:a) increase its speed            b) decrease its momentum
c) change the direction             d) keep it moving with uniform velocity

3) A body of mass 2 kg moving on a horizontal surface with an initial velocity of 4 m/s comes to rest after 2 sec. If one wants to keep this body moving on the same surface with a velocity of 4 m/s, the force required is:   {answer should come 4 N}

4) In the system shown in the figure(down) the tension T2 is:   {answer should come 5 g}

Answer 1

1) c
2) d
3) m = 2kg
u = 4m/s
v = 0m/s
t = 2sec
v = u + at
0 = 4 + a( 2 )
-4 = a ( 2)
a = -4/2
a = -2m/s²
F = ma
F = 2( 2 )
F = 4N

Answer 2

1. a)  there is no force acting on it.      and   also,
    c)  the combination of forces acting on it balance each other..
       both a and c  must be true.

2.  d) a force is not required to keep it moving with a uniform velocity. 
     a  force is needed for all other options.

3.   the deceleration caused by friction = a .
          a = (v-u)/t = 0-4 / 2 = -2 m/sec/sec
       frictional force = - 2 kg * 2 m/sec/sec = - 4 Newtons
         so a force of +4N is needed to cancel friction.  Then the body will continue at the uniform velocity of 4 m/sec

4)   
    The blocks of 1 kg, 2kg, and 3 kg are all in equilibrium - stationary - when there are acted up on by two or more forces on each block.   let g be acceleration due to gravity.

T1 and weight of block 3 kg are balancing.  Hence T1 = 3 * g  newtons.

T1,  T2 and weight of 2 kg block are acting on mass of 2 kg.  they are balanced.  T1 and weight are acting down wards.  T2 is upwards.

                 T1 + 2 * g = T2              =>  T2 = 3 g + 2 g  = 5 g  newtons
  
    T3, T2 and weight of 1 kg block are acting on mass of 1kg.
              T3 = T2 + 1 * g  = 6 * g  newtons.