Q: A rock is dropped from rest into a 20 m deep well. Neglecting air resistance, how long does it take to hit the bottom? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

$$t = \sqrt{\frac{2 \times 20}{9.8}} \approx 2.02\ \mathrm{s}$$

Q: A cyclist moves with a constant velocity of $$6\ \mathrm{m/s}$$ for 10 seconds. What is the total displacement?

$$x = v t = 6 \times 10 = 60\ \mathrm{m}$$

Question 1

A car moves along a straight road. Its position-versus-time graph is a straight line with a positive slope. Which of the following statements is true about the car's motion?

Accepted Answer

The car is moving at a constant velocity in the positive direction.

Question 2

Which of the following best describes the difference between distance and displacement?

Accepted Answer

Distance is a scalar and measures the total path length, while displacement is a vector and measures the straight-line change in position.

Question 3

A runner travels 100 m east, then 60 m west, in 20 seconds. What is the runner's average velocity?

Accepted Answer

$$v_{avg} = \frac{40\ \mathrm{m}}{20\ \mathrm{s}} = 2\ \mathrm{m/s}$$ east

Question 4

Which of the following statements about acceleration is correct?

Accepted Answer

Acceleration is the rate of change of velocity and can be caused by a change in speed or direction.

Question 5

A ball is thrown straight up. At the very top of its trajectory, which of the following is true?

Accepted Answer

The velocity is zero, but the acceleration is $$-9.8\ \mathrm{m/s^2$}.$$

Question 6

A car starts from rest and accelerates uniformly at $$2\ \mathrm{m/s^2$}$$ for 5 seconds. What is its final velocity?

Accepted Answer

$$v = v_0$ + a t = 0 + (2)(5) = 10\ \mathrm{m/s}$$

Question 7

A rock is dropped from rest into a 20 m deep well. Neglecting air resistance, how long does it take to hit the bottom? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$t = \sqrt{\frac{2 	imes 20}{9.8}} \approx 2.02\ \mathrm{s}$$

Question 8

Which of the following graphs best represents the velocity of an object in free fall (downward is positive) after being dropped from rest?

Accepted Answer

A straight line with positive slope starting at zero.

Question 9

A cyclist moves with a constant velocity of $$6\ \mathrm{m/s}$$ for 10 seconds. What is the total displacement?

Accepted Answer

$$x = v t = 6 	imes 10 = 60\ \mathrm{m}$$

Question 10

A car's velocity changes from $$+20\ \mathrm{m/s} to$$ $$-10\ \mathrm{m/s} in 5 $$seconds. What is its average acceleration?

Accepted Answer

$$a_{avg} = \frac{-10 - 20}{5} = -6\ \mathrm{m/s^2$}$$

Question 11

A springbok leaps vertically upward with an initial velocity of $$8\ \mathrm{m/s}. $$What is the maximum height it reaches? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$h = \frac{v_0$^2}{2g} = \frac{8^2$}{2 	imes 9.8} \approx 3.27\ \mathrm{m}$$

Question 12

A sandbag is dropped from a hot air balloon rising at $$8\ \mathrm{m/s}. $$What is the sandbag's velocity 2 seconds after being released? (Take upward as positive, $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$v = 8 - 9.8 	imes 2 = 8 - 19.6 = -11.6\ \mathrm{m/s}$$

Question 13

Which of the following is true about the motion of two objects that have the same velocity at a given instant?

Accepted Answer

They are moving in the same direction with the same speed at that instant.

Question 14

A position-versus-time graph for an object is a curve that gets steeper with time. What does this indicate about the object's motion?

Accepted Answer

The object is speeding up; its velocity is increasing.

Question 15

A car moves with a constant acceleration of $$3\ \mathrm{m/s^2$}$$, starting from rest. How far does it travel in 4 seconds?

Accepted Answer

$$x = v_0$ t + \frac{1}{2} a t^2$ = 0 + 0.5 	imes 3 	imes 16 = 24\ \mathrm{m}$$

Question 16

Which of the following best describes the particle model in kinematics?

Accepted Answer

It treats a moving object as if all its mass is concentrated at a single point.

Question 17

A car is moving to the right and slowing down. What is the direction of its acceleration?

Accepted Answer

To the left (opposite to the direction of motion).

Question 18

If the velocity-versus-time graph of an object is a horizontal line above the time axis, what does this indicate?

Accepted Answer

The object is moving at a constant positive velocity.

Kinematics and Motion: Study Notes for Physics 1 (PCS 120)

Guida di studio - Domande di pratica

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