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Physics Chapter 3 : Test Yourself
1 / 9
A projectile thrown upward moves in its parabolic path, the velocity and acceleration vectors for the projectile are perpendicular to each other at:
Reasoning: In projectile motion, acceleration is always vertically downward due to gravity. At the highest point, the vertical velocity becomes zero, so the velocity is only horizontal. A horizontal velocity vector and vertical acceleration vector are perpendicular to each other.
2 / 9
A truck driving along a highway road has a large quantity of momentum. If it moves at the same speed but has twice as much mass, its momentum is _________.
Reasoning: Momentum is $\mathbf{p = mv}$. If speed remains the same but mass becomes twice, then momentum also becomes twice.
3 / 9
A $\mathbf{5\ N}$ force is applied to a $\mathbf{3\ kg}$ ball to change its velocity from $\mathbf{9\ }\mathbf{ms}^{\mathbf{- 1}}$ to $\mathbf{3\ }\mathbf{ms}^{\mathbf{- 1}}$. This impulse causes the momentum change of the ball to be ________ $\mathbf{kg\ }\mathbf{ms}^{\mathbf{- 1}}$.
Reasoning: Change in momentum is $\mathbf{\Delta p = m}\mathbf{(}\mathbf{v}_{\mathbf{f}}\mathbf{-}\mathbf{v}_{\mathbf{i}}\mathbf{)}$.$\mathbf{\Delta p = 3(3 - 9)}$ $\mathbf{\Longrightarrow}$ $\mathbf{\Delta p = 3( -}\mathbf{\ }\mathbf{6) = -}\mathbf{\ }\mathbf{18}\mathbf{\ }\mathbf{kg}\mathbf{ms}^{\mathbf{- 1}}$Negative sign shows that momentum decreased.
4 / 9
Which of the following statements is true about the projectile motion?
Reasoning: A projectile is any object thrown into the air that moves under the effect of gravity only after launch, ignoring air resistance. It can be thrown horizontally, vertically, or at an angle.
5 / 9
The vertical component of velocity of a projectile is smallest at:
Reasoning: The vertical component of velocity decreases as the projectile rises. At the highest point, vertical velocity becomes $\mathbf{V}_{\mathbf{y}}\mathbf{= 0}$. So, it is smallest at the top.
6 / 9
A $\mathbf{4\ kg}$ object has a momentum of $\mathbf{12\ kg\ }\mathbf{ms}^{\mathbf{- 1}}$. The object’s speed is _________ $\mathbf{m/s}$.
Reasoning: Momentum is $\mathbf{p = mv}$. $\mathbf{\Longrightarrow}$ $\mathbf{v =}$ $\frac{\mathbf{p}}{\mathbf{m}}$ $\mathbf{\Longrightarrow}$ $\mathbf{v =}$ $\frac{\mathbf{12}}{\mathbf{4}}\mathbf{= 3}\mathbf{\ }\mathbf{m}\mathbf{s}^{\mathbf{- 1}}$
7 / 9
A bomb of mass $\mathbf{9\ kg}$ explodes into $\mathbf{2}$ pieces of mass $\mathbf{3\ kg}$ and $\mathbf{6\ kg}$. The velocity of mass $\mathbf{3\ kg}$ is $\mathbf{1.6\ }\mathbf{ms}^{\mathbf{- 1}}$, the kinetic energy of mass $\mathbf{6\ kg}$ is _________.
Reasoning: Before explosion, total momentum is zero.So after explosion, $\mathbf{\Longrightarrow}$ $\mathbf{m}_{\mathbf{1}\mathbf{\ }}\mathbf{v}_{\mathbf{1}}\mathbf{+}\mathbf{m}_{\mathbf{2}\mathbf{\ }}\mathbf{v}_{\mathbf{2}}\mathbf{= 0}$$\mathbf{3(1.6) + 6}\mathbf{\ }\mathbf{v}_{\mathbf{2}}\mathbf{= 0}$ $\mathbf{\Longrightarrow}$ $\mathbf{4.8 + 6}\mathbf{\ }\mathbf{v}_{\mathbf{2}}\mathbf{= 0}$ $\mathbf{\Longrightarrow}$ $\mathbf{v}_{\mathbf{2}}\mathbf{= -}\mathbf{\ }\mathbf{0.8}\mathbf{\ }\mathbf{m}\mathbf{s}^{\mathbf{- 1}}$Now kinetic energy of $\mathbf{6\ kg}$ mass:$\mathbf{K.E =}$ $\frac{\mathbf{1}}{\mathbf{2}}$ $\mathbf{m}\mathbf{v}^{\mathbf{2}}$ $\mathbf{\Longrightarrow}$ $\mathbf{K.E =}$ $\frac{\mathbf{1}}{\mathbf{2}}\mathbf{(6)}\mathbf{(0.8)}^{\mathbf{2}}$$\mathbf{K.E = 3(0.64) = 1.92}\mathbf{\ }$J
8 / 9
What is the force experienced by a projectile after the initial force that launched it into the air in the absence of air resistance?
Reasoning: After the projectile is launched, and air resistance is ignored, the only force acting on it is gravity. Gravity pulls it downward throughout the motion.
9 / 9
If a projectile is launched on level ground, what launch angle maximizes the range of the projectile?
Reasoning: For a projectile launched on level ground, range is maximum when the launch angle is $\mathbf{45}^{\mathbf{o}}$. At this angle, horizontal and vertical components give the best combination for maximum distance.
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