Question

Choose te right option an give reason
1. When a bdy is stationary:
a) there is no force acting o it
b) the forces actng on i are not in contact with it
c) the combination of force 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 forcerequired is:
a) 8 N
b) 4 N
c) zero
d) 2 N

Answer 1

1)  a and  c

2)  d

3)     change in momentum of the body = 2 kg (0 - 4)m/s = - 8 kg-m/s
        friction force = change in momentum / duration = (-8 kg-m/sec ) / 2 sec
                = - 4 Newtons
       force needed to maintain the uniform velocity of 4 m/s from the beginning is
        = + 4 Newtons, in the direction of movement of the body.