Revision Quiz Topic 2.2

Which of the following is the condition for a body to be in translational equilibrium?

• The resultant force on the body in any direction is zero.

• The velocity of the body in any direction is zero.

• No external force is acting on the body.

• No work is done on the body.

The initial kinetic energy of a block moving on a horizontal floor is 48 J. A constant frictional force acts on the block bringing it to rest over a distance of 2 m. What is the frictional force on the block?

• 24 N

• 48 N

• 96 N

• 192 N

A motor of input power 160 W raises a mass of 8.0 kg vertically at a constant speed of 0.50 m s^–1.

What is the efficiency of the system?

• 0.63%

• 25%

• 50%

• 100%

Two identical spheres, each of mass m and speed v, travel towards each other on a frictionless surface in a vacuum. The spheres undergo a head-on elastic collision.

Which statement correctly describes the spheres after the collision?

• The total momentum of the spheres is 2mv.

• Each sphere has zero momentum.

• The total kinetic energy of the spheres is mv².

• Each sphere has zero kinetic energy.

The net force on a body is F. The impulse of F is equal to the

• change in momentum of the body.

• rate of change of momentum of the body.

• change of kinetic energy of the body.

• change of total energy of the body.

The efficiency of an electric motor is 20 %. When lifting a body 500 J of energy are wasted. What is the useful work done by the motor?

• 100 J

• 125 J

• 250 J

• 400 J

A stone is falling at a constant velocity vertically down a tube filled with oil. Which of the following statements about the energy changes of the stone during its motion are correct?

I. The gain in kinetic energy is less than the loss in gravitational potential energy.

II. The sum of kinetic and gravitational potential energy of the stone is constant.

III. The work done by the force of gravity has the same magnitude as the work done by friction.

• I and II only

• I and III only

• II and III only

• I, II and III

Which of the following is always true for an object moving in a straight line at constant speed?

• No forces act on the object.

• No resultant force acts on the object.

• The momentum of the object is zero.

• No work is being done on the object.

A student makes three statements about situations in which no work is done on an object.

I. The object is moving with uniform circular motion.

II. A force is applied to the object in the direction of its velocity.

III. A force is applied to the object in a direction opposite to its motion.

Which of the above statements is/are correct?

• I only

• I and II only

• I and III only

• III only

Objects A and B collide together. They end up joined together and stationary. During the collision, a force +F is exerted on object A by object B. According to Newton’s third law, there will also be a force of

• -F acting on object B.

• -F acting on object A.

• +F acting on object B.

• +F acting on object A.