GRADE 9 PRACTICE
Physics Problems: Momentum, Grade 9
Body impulse and force, collisions and jet motion.
Here the conditions and analysis of the solution can be read without an account. In the simulator, you need to collect the same analyzes yourself: “Given,” formulas, order of steps and answer.
Problem statements
The answer options are there to check against, and the walkthrough opens under each problem.
Problem #22
Momentum and rocket propulsionWhat concept does the description correspond to: “The product of the average force and the time of action is equal to the change in the momentum of the body.”?
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- \text{Description}
- \text{Average force multiplied by its duration equals the body's momentum change.}
\text{name concepts} - ?
- \text{Let's compare approval with definition}
A longer stopping time reduces the average force for the same momentum change; airbags use this principle.
- \text{Let's formulate conclusion}\text{Concept} = \text{Impulse}
Answer\text{Concept} = \text{Impulse}
Problem #23
Momentum and rocket propulsionWhat concept does the description correspond to: “The total momentum of a closed system remains constant during internal interactions.”?
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- \text{Description}
- \text{The total momentum of an isolated system remains constant during internal interactions.}
\text{name concepts} - ?
- \text{Let's compare approval with definition}
The law describes collisions, recoil and rocket propulsion through ejection of mass.
- \text{Let's formulate conclusion}\text{Concept} = \text{Conservation of momentum}
Answer\text{Concept} = \text{Conservation of momentum}
Problem #24
MomentumA cart with a mass of 2 kg moves at a speed of 3 m/s and is coupled to a cart with a mass of 1 kg at rest. Find the overall speed.
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- m_1
- 2\,\text{кг}
- v_1
- 3\,\text{м/с}
- m_2
- 1\,\text{кг}
- v_2
- 0
v - ?
- m_1v_1+m_2v_2=(m_1+m_2)v
- v=\frac{m_1v_1}{m_1+m_2}v=\frac{2\cdot3}{2+1}\,\text{м/с}v = 2\,\text{м/с}
Answer2\,\text{м/с}
Problem #106
Momentum and rocket propulsionObject mass 3 kg, speed 5 m/s. Find the modulus of the impulse.
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- m
- 3\,\text{кг}
- v
- 5\,\text{м/с}
p - ?
- p=mvp=3 \cdot 5p=15\,\text{кг·м/с}
The impulse is directed in the same way as the speed.
Answer15\,\text{кг·м/с}
Problem #107
Momentum and rocket propulsionObject mass 4 kg, speed 7 m/s. Find the modulus of the impulse.
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- m
- 4\,\text{кг}
- v
- 7\,\text{м/с}
p - ?
- p=mvp=4 \cdot 7p=28\,\text{кг·м/с}
The impulse is directed in the same way as the speed.
Answer28\,\text{кг·м/с}
Problem #108
Momentum and rocket propulsionTrolley weight 2 kg moves with speed 6 m/s and engages with a stationary trolley mass 4 kg. Find the overall speed. Neglect external impulse.
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- m_1
- 2\,\text{кг}
- m_2
- 4\,\text{кг}
- v
- 6\,\text{м/с}
u - ?
- p=m_1vp=2 \cdot 6p=12\,\text{кг·м/с}
Before the impact, only the first cart moves.
- u=\frac{p}{m_1+m_2}u=\frac{12}{(2 + 4)}u=2\,\text{м/с}
After coupling, the momentum belongs to the total mass.
Answer2\,\text{м/с}
Problem #109
Momentum and rocket propulsionTrolley weight 3 kg moves with speed 8 m/s and engages with a stationary trolley mass 3 kg. Find the overall speed. Neglect external impulse.
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- m_1
- 3\,\text{кг}
- m_2
- 3\,\text{кг}
- v
- 8\,\text{м/с}
u - ?
- p=m_1vp=3 \cdot 8p=24\,\text{кг·м/с}
Before the impact, only the first cart moves.
- u=\frac{p}{m_1+m_2}u=\frac{24}{(3 + 3)}u=4\,\text{м/с}
After coupling, the momentum belongs to the total mass.
Answer4\,\text{м/с}
Problem #110
Momentum and rocket propulsionCarts by the masses 4 and 2 kg are moving towards at speeds 5 and 4 m/s and interlock. Find the modulus of the overall speed. The positive direction coincides with the movement of the first cart.
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- m_1
- 4\,\text{кг}
- m_2
- 2\,\text{кг}
- v_1
- 5\,\text{м/с}
- v_2
- 4\,\text{м/с}
u - ?
- p_1=m_1v_1p_1=4 \cdot 5p_1=20\,\text{кг·м/с}
The first impulse is positive.
- |p_2|=m_2v_2|p_2|=2 \cdot 4|p_2|=8\,\text{кг·м/с}
The second impulse is directed opposite to the first.
- u=\frac{p_1-|p_2|}{m_1+m_2}u=\frac{(20 - 8)}{(4 + 2)}u=2\,\text{м/с}
In these data, the final impulse is directed along the movement of the first cart.
Answer2\,\text{м/с}
Problem #111
Momentum and rocket propulsionCarts by the masses 5 and 3 kg are moving towards at speeds 6 and 2 m/s and interlock. Find the modulus of the overall speed. The positive direction coincides with the movement of the first cart.
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- m_1
- 5\,\text{кг}
- m_2
- 3\,\text{кг}
- v_1
- 6\,\text{м/с}
- v_2
- 2\,\text{м/с}
u - ?
- p_1=m_1v_1p_1=5 \cdot 6p_1=30\,\text{кг·м/с}
The first impulse is positive.
- |p_2|=m_2v_2|p_2|=3 \cdot 2|p_2|=6\,\text{кг·м/с}
The second impulse is directed opposite to the first.
- u=\frac{p_1-|p_2|}{m_1+m_2}u=\frac{(30 - 6)}{(5 + 3)}u=3\,\text{м/с}
In these data, the final impulse is directed along the movement of the first cart.
Answer3\,\text{м/с}
The theory behind these problems
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Formulas by topic
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