The force of friction is <u>34.3 N.</u>
A block of mass m slides down a plane inclined at an angle θ to the horizontal with a constant velocity. According to Newton's first law of motion, every body continues in its state of rest or a state of uniform motion in a straight line, unless acted upon, by an external unbalanced force. This means that when balanced forces act on a body, the body moves with a constant velocity.
The free body diagram of the sliding block is shown in the attached diagram. Resolve the weight mg of the block into two components mg sinθ along the direction of the plane and mg cosθ perpendicular to the plane . The force of friction F acts upwards along the plane and the normal reaction acts perpendicular to the plane.
Since the block moves down with a constant velocity, the downward force mg sinθ must be equal to the upward frictional force.
Substitute 7 kg for m, 9.8 m/s² for g and 30° for θ.
The force of friction is <u>34.3 N</u> up the plane.
14. Answer;
-There are two potassium ions for each ion of sulfur.
Explanation;
The formula K2S indicates that there are two potassium ions for each ion of sulfur.
-K2S is the formula of potassium sulfide.
- From the formula; two potassium atoms combines with 1 atom of sulfur to form the compound. In other words the ratio of potassium and sulfur atoms in the compound is 2 : 1.
15. Answer;
-Lithium fluoride
Explanation;
-Fluorine, F, forms a binary ionic compound with lithium, Li. The name of the compound is lithium fluoride.
- A compound is a substance that is formed when two or more atoms from different elements are chemically bonded. For example Lithium fluoride is a compound that is made of fluorine atom and lithium atom that are chemically combined.
16. Answer;
-Carbon-12 atom
Explanation;
The standard on which the atomic mass unit is based is the mass of a carbon-12 atom.
-Atomic mass is the quantity of matter contained in an atom of an element. -The atomic mass is expressed as a multiple of one-twelfth the mass of the carbon-12 atom, which is assigned an atomic mass of 12 units.
17. Answer;
- Non-metal fluorine
Explanation;
-Two highly reactive elements in Period 2 are the metal lithium and the non-metal fluorine.
-Elements in period 2 often have the most extreme properties in their respective groups. Fluorine is the most reactive halogen, neon is the most inert noble gas, and lithium is the least reactive alkali metal, but the most reactive metal in group 2.