Mechanical Engineering Principles

FORCE, MASS AND ACCELERATION 151

6. State Newton’s second law of motion.


7. Define the Newton.


8. State Newton’s third law of motion.


9. Explain why an object moving round a
   circle at a constant angular velocity has
   an acceleration.


10. Define centripetal acceleration in sym-
    bols.


11. Define centripetal force in symbols.


12. Define mass moment of inertia.


13. A rigid body has a constant angular
    acceleration α when subjected to a
    torqueT. The mass moment of inertia,
    Io=.......

Exercise 67 Multi-choice questions on
force, mass and acceleration
(Answers on page 284)

1. The unit of force is the:

(a) watt (b) kelvin

(c) newton (d) joule

2. Ifa=acceleration andF=force, then
   mass m is given by:

(a)m=a−F (b)m=

F

a

(c)m=F−a (d)m=

a

F

3. The weight of an object of mass 2 kg at
   a point on the earth’s surface when the
   gravitational field is 10 N/kg is:

(a) 20 N (b) 0.2 N

(c) 20 kg (d) 5 N

4. The force required to accelerate a loaded
   barrow of 80 kg mass up to 0.2 m/s^2 on
   friction-less bearings is:

(a) 400 N (b) 3.2 N

(c) 0.0025 N (d) 16 N

5. A bucket of cement of mass 30 kg is tied
   to the end of a rope connected to a hoist.
   If the gravitational fieldg=10 N/kg,

the tension in the rope when the bucket

is suspended but stationary is:

(a) 300 N (b) 3 N

(c) 300 kg (d) 0.67 N

A man of mass 75 kg is standing in a

lift of mass 500 kg. Use this data to

determine the answers to questions 6 to

9. Takegas 10 m/s^2


10. The tension in a cable when the lift is
    moving at a constant speed vertically
    upward is:

(a) 4250 N (b) 5750 N

(c) 4600 N (d) 6900 N

7. The tension in the cable supporting the
   lift when the lift is moving at a constant
   speed vertically downwards is:

(a) 4250 N (b) 5750 N

(c) 4600 N (d) 6900 N

8. The reaction force between the man and
   the floor of the lift when the lift is
   travelling at a constant speed vertically
   upwards is:

(a) 750 N (b) 900 N

(c) 600 N (d) 475 N

9. The reaction force between the man and
   the floor of the lift when the lift is
   travelling at a constant speed vertically
   downwards is:
   (a) 750 N (b) 900 N
   (c) 600 N (d) 475 N
   A ball of mass 0.5 kg is tied to a thread
   and rotated at a constant angular velocity of
   10 rad/s in a circle of radius 1 m. Use this
   data to determine the answers to questions 10
   and 11


10. The centripetal acceleration is:

(a) 50 m/s^2 (b)

100

2 π

m/s^2

(c)

50

2 π

m/s^2 (d) 100 m/s^2

11. The tension in the thread is:

(a) 25 N (b)

50

2 π

N

(c)

25

2 π

N (d) 50 N