Deck 14: Frictional Resistance

Question 1

Decide whether each of these statements is True (T) or False
A horizontal force of 100 N acts on a block of mass 3 kg resting on a horizontal surface where the static
Coefficient of friction is 0.5. The acceleration due to gravity is 9.8 m/s2.
(i) The normal reaction force is 29.4 N.
(ii) The limiting frictional force is 14.7 N.

A) (i) T (ii) T
B) (i) T (ii) F
C) (i) F (ii) T
D) (i) F (ii) F

Answer 1

A

Question 2

Decide whether each of these statements is True (T) or False
The angle of friction is the angle:
(i) Between the reaction force and the plane on which an object is sliding.
(ii) The angle at which an incline needs to be for sliding to begin to occur

A) (i) T (ii) T
B) (i) T (ii) F
C) (i) F (ii) T
D) (i) F (ii) F

Answer 2

C

Question 3

Decide whether each of these statements is True (T) or False
An object of mass m rests on an inclined plane at angle Ï´ to the horizontal. If g is the acceleration due to gravity:
(i) The normal reaction force is mg cos Ï´.
(ii) The component of the force down the plane is mg sin Ï´.

A) (i) T (ii) T
B) (i) T (ii) F
C) (i) F (ii) T
D) (i) F (ii) F

Answer 3

A

Question 4

An object of mass 3 kg rests on a horizontal plane and is pulled along the plane by a force of 15 N at an angle of 30º to the plane. The acceleration due to gravity is 9.8 m/s2. If this force is just sufficient to start motion, the coefficient of static friction is:

A) 0.09
B) 0.44
C) 0.57
D) 0.59

Question 5

A single-start screw thread has a pitch of 5 mm and a mean diameter of 20 mm. The helix angle is:

A) 2.3·
B) 4.6·
C) 9.0·
D) 57.9·