Chapter 11 study guide answers: remember to show all work on the study guide for credit



118. it will decrease

119. f= m(a) is Newton’s second law of motion

120. Third law of motion

121. the toy train has less momentum than the real train because the toy train has less mass

122. This example shows balanced forces.

123. f= m(a); 15kg * 3m/s2 =45N

124. The total momentum of an isolated system does not change. (Law of Conservation of Momentum) Another way of stating this is that the initial momentum of an isolated system is equal to its final momentum. This will help you answer a). and b).



1. You actually need to know the momentum to do this equation. p= m (v).

p= 1kg * 4m/s; p= 4kg*m/s So now you can take the momentum—due to the fact of the law of conservation of momentum and apply it to the equation (v= p/m) for a.

v= (4kg*m/s)/2kg; v=2m/s across the floor.



2. We already found (b) p=m(v); p= 1kg * 4m/s therefore p= 4kg*m/s



125. The unit for force is called the Newton (N).

126. inertia. An object in motion will stay in motion or an object at rest will stay at rest unless at outside force acts upon it.

127. From the example: the feather has the lease inertia and the elephant has the most. The more mass the more inertia.

128. inertia. An object in motion will stay in motion or an object at rest will stay at rest unless at outside force acts upon it.

129. If the same force is applied—the golf ball will have the most acceleration and the bowling ball will have the lease acceleration.

130. Three ways to reduce friction: smooth out the surfaces, add a lubricant (such as oil or grease), or add rollers.

131. The mass of the box—meaning the box is too heavy. The floor is too bumpy or rough. Another reason--- microwelds (small uneven surfaces) may have formed between the bottom of the box and the floor---- think of it like sliding the box on sand paper. Even though a surface may look smooth, if you magnify the surface it isn’t smooth. Everything is made of molecules. The molecules come together to make bumps. Some surfaces have molecules that leave large bumps and some leave smaller bumps, but all surfaces have bumps. Microwelds occur when two bumpy surfaces are rubbed up against each other they stick together.

132. Helpful friction: braking, walking on ice. Not helpful: skating, gears, trying to move objects, wearing away of engine parts

133. A. 15N; B. 5N

134. The parachute allows for air resistance to slow him down to a safe enough velocity to land.

135. a. 2000kg * 4m/s= 8000 kg*m/s use significant figures--- which is 1: (8 * 103 kg*m/s)

b. 0.2kg * 500m/s= 100kg*m/s use significant figures--- which is 1: (1 * 102 kg*m/s)

c. 0.75kg * 16m/s = 12kg*m/s use significant figures--- which is 2: (12 kg*m/s)

d. 6kg * 8m/s = 48 kg*m/s use significant figures--- which is 1: (5 * 102 kg*m/s)



Chapter 12 study guide answers

136. use 9.8 m/s2 for (g)—unless the equation states otherwise.

{GPE= mgh} 0.310kg * 9.8 m/s2 *680 m = 2065.85J but you must follow significant figure rule and there are two—so the answer is 2.1 * 103J put the answer in scientific notation.



137. KE= 1/2(m) * (v)2: ½ (900kg) * (8m/s)2 = 450kg * 64m/s = KE = 28800 J: put the answer in significant figures and there is only 1 so the answer is 3*104 J remember to use the rules of rounding.



138. The coin has the most potential energy (PE) at the point it is tossed from the building

139. The coin has the most kinetic energy (KE) right before it hits the ground.

140. As KE increases PE decreases

141. a).The cannonball has the greatest KE at point E; b). greatest PE at point C; c). from a to c kinetic energy gets smaller as potential energy gets larger; d). from c to e potential gets smaller as kinetic energy gets larger.

142. The SI unit for energy is the Joule (J)

143. Kinetic energy because the truck is moving. But mechanical energy could also be an answer.

144. Friction is nonmechanical energy

145. Law of conservation of energy states that energy cannot be created or destroyed.

146. In the sun solar energy releases heat and light. Strawberry plants us the light energy through photosynthesis and store and food in the form of chemical potential energy. The guy goes for a bicycle ride and as he pushes the pedals, kinetic energy is converted to mechanical energy. As he nears the tops of a hill, the kinetic energy is converted to potential energy. As he goes down the other side of the hill the potential energy is converted to kinetic energy, the energy of motion.