Unit 2: Force and Translational Dynamics
Weightage : 20-15%
A \(1\,\mathrm{kg}\) block hangs from a string at rest. A person holds a spring scale attached vertically to the string, pulling upward so that the scale reads \(10\,\mathrm{N}\).
What is the tension in the string?
Correct Answer: \( \boxed{\mathrm{D}} \)
The block is at rest, so it is in static equilibrium. Therefore, the net force on the block is zero.
Applying Newton’s first law,
\(\sum F_y=0\)
\(T-mg=0\)
Thus,
\(T=mg=(1\,\mathrm{kg})(10\,\mathrm{m/s^2})=10\,\mathrm{N}\)
A spring scale measures the tension in the string. Since the scale reads \(10\,\mathrm{N}\), the tension throughout the string is \(10\,\mathrm{N}\).
Therefore, the correct answer is (D).
While standing on a moving train, you are suddenly thrown forward as the train stops. This effect can be best explained using Newton’s law of
Correct Answer: \( \boxed{\mathrm{A}} \)
Newton’s First Law, also known as the law of inertia, states that an object in motion tends to remain in motion with the same velocity unless acted upon by a net external force.
Before the train stops, both you and the train are moving forward with the same velocity.
When the train suddenly stops, the train experiences a backward acceleration due to an external force, but your body tends to continue moving forward because of its inertia.
As a result, you appear to be thrown forward relative to the train until a force from the floor, seat, or another object brings you to rest.
This phenomenon is a direct consequence of the tendency of objects to resist changes in their state of motion.
Therefore, the effect is best explained by Newton’s law of
\( \boxed{\text{inertia}} \).
After throwing a ball at an upward angle, the reason the ball continues to go horizontally while falling due to gravity is that
Correct Answer: \( \boxed{\mathrm{A}} \)
According to Newton’s First Law, an object in motion continues moving with constant velocity unless acted upon by a net external force.
After the ball leaves the thrower’s hand, the force of the throw no longer acts on the ball.
Neglecting air resistance, the only force acting on the ball is gravity, which acts vertically downward.
Since there is no horizontal force, the horizontal component of the ball’s velocity remains constant.
Gravity changes only the vertical component of the motion, causing the ball to accelerate downward while continuing to move horizontally.
This persistence of horizontal motion is due to the ball’s inertia, which is its tendency to resist changes in motion.
Choice (B) is incorrect because the force of the throw acts only while the ball is in contact with the hand.
Choice (C) incorrectly describes energy transfer, and choice (D) is unrelated to the horizontal motion.
Therefore, the ball continues moving horizontally because
\( \boxed{\text{its inertia keeps it going}} \).
