(a)(i) State the law of inertia.
(ii) Use the law stated in (a)(I) to explain how wearing a safety belt in a moving vehicle could reduce the possibilities of severe injuries when the vehicle is involved in a collision.
(b)(I) Define the term moment of a force.
(ii) A uniform plank measures 2 m long from its ends point A to point B. If the weight of the plank is 54 N and it rests on a knife edge 0.50 m from end B and point A is supported by a vertical string so that AB balances horizontally:
i. Draw a force diagram for the arrangement;
ii. Determine the tension, T, in the string.
iii. Determine the force, F, acting on the knife edge
(c) State three differences between solid friction and viscosity
(d) State one method of increasing the velocity ration of a pulley system.
Explanation
(a) (i) The Law of Inertia states that: A body continues in its state of rest or uniform linear motion unless acted upon by an external force to act otherwise.
(ii) Explanation of wearing safety: The safety belt acts as an external force that prevents a passenger from an otherwise forward motion after impact.
(b)(i)Mmoment of a force: The product of a force and the perpendicular distance from a reference point to the line of action of the force.
(b)(ii) Force diagram:
(ii) Determination of the tension, T, in the string;
Taking moment about the knife edge
Sum of clockwise moment = sum of anti-clockwise moment.
T x 1.5 = 54 x 0.5
\(\therefore\) T = 18 N
(ii) Determination of the force, F, acting the knife edge;
At equilibrium, the sum of upward forces = the sum of forces acting downward
T + F = 54
T = 18 N
18 + F = 54
F = 36 N
| Solid friction | Viscosity |
| It occurs on solid surfaces | It occurs within fluids |
| It is independent of areas of surfaces on | It depends on the area of the surfaces in |
| It depends on the speed of motion of the surface in contact | It is independent of the speed of motion of the surfaces in contact |
| It is independent of temperature | It depends on the temperature |
| It depends on the normal reaction. | It is independent of normal reaction |
(d)Increasing the number of pulleys