Laws of Motion · Question 7

A bob is whirled in a horizontal plane by means of a string with an initial speed of rpm. The tension in the string is T. If speed becomes 2 while keeping the same radius, the tension in the string becomes:

1. T
2. 4T
3. T4
4. 2T

A bob is whirled in a horizontal circle by means of a string at an initial speed of 10 rpm. If the tension in the string is quadrupled while keeping the radius constant, the new speed is:

1. 20 rpm
2. 40 rpm
3. 5 rpm
4. 10 rpm

A box of mass 5 kg is pulled by a cord, up along a frictionless plane inclined at 30 with the horizontal. The tension in the cord is 30 N. The acceleration of the box is (Take g = 10 m s-2)

1. 2 m s-2
2. Zero
3. 0.1 m s-2
4. 1 m s-2

A football player is moving southward and suddenly turns eastward with the same speed to avoid an opponent. The force that acts on the player while turning is :

1. along northward
2. along north-east
3. along south-west
4. along eastward

Calculate the maximum acceleration of a moving car so that a body lying on the floor of the car remains stationary. The coefficient of static friction between the body and the floor is 0.15 (g = 10 m s-2 ).

1. 150 m s-2
2. 1.5 m s-2
3. 50 m s-2
4. 1.2 m s-2

A shell of mass m is at rest initially. It explodes into three fragments having mass in the ratio 2 : 2 : 1. If the fragments having equal mass fly off along mutually perpendicular directions with speed v, the speed of the third (lighter) fragment is :

1. v
2. 2v
3. 2 2v
4. 3 2v

The distance covered by a body of mass 5 g having linear momentum 0.3 kg m/s in 5 s is :

1. 0.3 m
2. 300 m
3. 30 m
4. 3 m

In the diagram shown, the normal reaction force between 2 kg and 1 kg is (Consider the surface, to be smooth) : (Given g = 10 m s-2) [figure]

1. 10 N
2. 25 N
3. 39 N
4. 6 N

A ball of mass 0.15 kg is dropped from a height 10 m, strikes the ground and rebounds to the same height. The magnitude of impulse imparted to the ball is (g = 10 m/s2) nearly :

1. 1.4 kg m/s
2. 0 kg m/s
3. 4.2 kg m/s
4. 2.1 kg m/s

Two bodies of mass 4 kg and 6 kg are tied to the ends of a massless string. The string passes over a pulley which is frictionless (see figure). The acceleration of the system in terms of acceleration due to gravity (g) is : [figure]

1. g/2
2. g/5
3. g/10
4. g