04b force practice test -...
TRANSCRIPT
I. VOCABULARY – Correct each sentence by changing only the underlined words.
1. Objects stay at rest or at constant speed in a straight line because of their energy. 2. Force is equal to mass multiplied by velocity. 3. Since a force is part of an interaction between two bodies, forces always come in triples. 4. An object in equilibrium has constant net force and decreasing acceleration. 5. Mass is a measure of the amount of weight in an object.
II. NET FORCE 6. A block is acted on by two forces. IV. MULTIPLE CHOICE 8. A student pushes a 6 kg textbook with 12 N of force. What is the force of the textbook pushing on the student’s hand?
A 0 N C 12 N B 2 N D 24 N
9. A 20 kg child on roller skates is pushed with a force of 39 N. What is the acceleration of the child during the push?
A 0.49 m/s² C 1.95 m/s² B 0.51 m/s² D 2.05 m/s²
V. WORD PROBLEMS 10. At the Sun’s surface, a 100 kg mass will have a weight of 2.5×10! N. What is the acceleration of gravity at the sun’s surface?
11. The wheels of a race car push the ground with 36 kN giving an acceleration of 40 m/s². What is the mass of the race car?
10 N 6 N 8 kg
What is the block’s…
Name: _______________________
Date: ___________ Period: _____ Force Practice Test
(a) net force? (b) acceleration?
III. MASS VS. WEIGHT 7. Fill in the missing information on the table.
Location weight mass acceleration of gravity
Earth 80 kg
Mars 4 m/s²
Jupiter 1600 N
Answers: 1) inertia 2) mass, acceleration 3) two, pairs 4) zero, zero 5) material 6) a. 4N, b. 0.5m/s² 7) Earth: 800N, 80kg, 10m/s²; Mars: 320N, 80kg, 4m/s²; Jupiter: 1600N, 80kg, 20m/s² 8) C 9) C 10) 250m/s² 11) 900kg
Force Study Guide
MAJOR CONCEPTS:
→ If a net force is applied to an object, the object will accelerate. (change speeds)
→ Inertia is the tendency for mass to resist a change in its motion (to remain the same).
→ Force is equal to mass multiplied by
acceleration. 𝐹 = 𝑚𝑎 → To every action there is always an equal and
opposed reaction. 𝐹!" = −𝐹!" → Weight is the force of gravity, it comes from
BOTH mass and gravity. (not just mass) → The acceleration of gravity on Earth is
9.8 m/s² (rounded off to 10 m/s²). EXAMPLE WORD PROBLEMS
quantity: x v t F m a
unit: m m/s s N kg m/s²
Ex1. The 400 kg Deep Space 1 spacecraft has a constant acceleration of 20 µm/s². What force is provided to the spacecraft by its ion thruster engines?
𝐹 = 𝑚 𝑎
𝐹 = 400 (20×10!!)
𝐹 = 8×10!!!!
𝐹 = 8×10!! N
Ex2. On the surface of a neutron star a 60 kg person would weigh 4.2×10!" N. What is the acceleration of gravity on a neutron star?
NEWTON’S LAWS OF MOTION
1st Law: When forces are balanced, no acceleration occurs; thus an object continues to move at constant velocity or stays at rest. 2nd Law: Acceleration is proportional to force and always points in the same direction as the force. (𝐹 = 𝑚𝑎) 3rd Law: When one object exerts a force on a second object, the second object always exerts a force on the first of equal magnitude and in the opposite direction.
FORCE FORMULAS
𝐹 Newton’s 2nd Law
= 𝑚 𝑎 force mass acceleration [N] [kg] [m/s²]
𝑤 Weight Formula
= 𝑚 𝑔 weight mass acceleration of
gravity [N] [kg] [m/s²]
MASS VS. WEIGHT
Weight is directly proportional to mass, but it is not equal to mass. Mass is a measure of the amount of material in an object, whereas weight is a measure of the gravitational force on an object. In places with less gravitational acceleration, the weight of an object will decrease, but the mass will still be the same.
NET FORCE PROBLEMS
net F = (4) + (-‐6) = -‐2 N
-‐4 N +6 N
net F = (-‐4) + (6) = 2 N
+4 N -‐6 N
The net force is the sum of all the forces.
𝑤 = 𝑚 𝑔
(4.2×10!")
6×10! = (60)𝑔60
𝑔 =426 ×10!"!! m/s²
𝑔 = 7×10!" m/s²
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