Chapter 1 Quizzes | Topic 1 Forces and Motion

Quiz 1 of 5 · Specification 1.1, 1.4, 1.6, 1.10

Kinematics — speed, acceleration and equations

1. A car travels at $54\,\text{km/h}$. What is this speed in m/s? A. $54\,\text{m/s}$ B. $194\,\text{m/s}$ C. $15\,\text{m/s}$ D. $1.5\,\text{m/s}$

Divide by 3.6: $54 / 3.6 = 15\,\text{m/s}$.

2. A student walks $240\,\text{m}$ in $80\,\text{s}$. What is the average speed? A. $0.33\,\text{m/s}$ B. $3.0\,\text{m/s}$ C. $3.2\,\text{m/s}$ D. $19200\,\text{m/s}$

$v = d/t = 240/80 = 3.0\,\text{m/s}$.

3. A trolley changes speed from $5.0\,\text{m/s}$ to $17.0\,\text{m/s}$ in $4.0\,\text{s}$. What is its acceleration? A. $3.0\,\text{m/s}^2$ B. $4.0\,\text{m/s}^2$ C. $5.5\,\text{m/s}^2$ D. $12.0\,\text{m/s}^2$

$a=(v-u)/t=(17.0-5.0)/4.0=3.0\,\text{m/s}^2$. D is $\Delta v$ without dividing by time.

4. A ball is released from rest and accelerates at $2.0\,\text{m/s}^2$ over $16\,\text{m}$. What is its final speed? A. $4.0\,\text{m/s}$ B. $6.0\,\text{m/s}$ C. $18\,\text{m/s}$ D. $8.0\,\text{m/s}$

$u=0$, so $v^2=2as=2(2.0)(16)=64$, $v=8.0\,\text{m/s}$. A is $\sqrt{16}$. C forgets the square root.

5. Which of these is a scalar quantity? A. velocity B. acceleration C. force D. speed

Speed has magnitude only. Velocity, acceleration and force all have direction.

Quiz 2 of 5 · Specification 1.3, 1.7–1.9

Distance–time and velocity–time graphs

1. A horizontal line on a distance–time graph means the object is A. moving at constant speed B. stationary C. accelerating D. moving at $0\,\text{m}$ per second of acceleration

Distance is not changing, so speed (the gradient) is zero. A horizontal line on a velocity–time graph would mean constant velocity.

2. The gradient of a velocity–time graph is equal to A. acceleration B. distance travelled C. average speed D. resultant force

1.8: gradient $= \Delta v / \Delta t = a$. Distance is the area under the line (1.9).

3. On a velocity–time graph, a horizontal line at $12\,\text{m/s}$ means the object is A. stationary B. accelerating at $12\,\text{m/s}^2$ C. moving at constant velocity D. $12\,\text{m}$ from the start

Gradient is zero, so $a=0$, but $v=12\,\text{m/s}$, so it is still moving. Stationary would be $v=0$.

4. A $v$–$t$ graph rises in a straight line from $0$ to $15\,\text{m/s}$ in $5.0\,\text{s}$. The acceleration is A. $0.33\,\text{m/s}^2$ B. $3.0\,\text{m/s}^2$ C. $15\,\text{m/s}^2$ D. $75\,\text{m/s}^2$

$a=15/5.0=3.0\,\text{m/s}^2$. D is $v \times t$, which is an area, not a gradient.

5. A cyclist travels at a constant $12\,\text{m/s}$ for $6.0\,\text{s}$. The area under this part of the $v$–$t$ graph is A. $72\,\text{m}$ B. $2.0\,\text{m}$ C. $18\,\text{m}$ D. $0\,\text{m}$, because acceleration is zero

Rectangle: $12 \times 6.0 = 72\,\text{m}$. Zero acceleration does not mean zero distance.

Quiz 3 of 5 · Specification 1.11–1.18

Forces, resultant force, $F=ma$ and weight

1. A force can change an object’s A. mass only B. temperature only C. speed, shape or direction D. gravitational field strength

Specification 1.11: forces change speed, shape or direction.

2. Friction is a force that A. always acts downwards B. opposes motion C. is a scalar quantity D. only acts on vehicles

1.16: friction opposes motion. It is a vector (a force) and acts in many situations, not just cars.

3. Forces of $30\,\text{N}$ right and $12\,\text{N}$ left act on a box. The resultant force is A. $18\,\text{N}$ to the right B. $18\,\text{N}$ to the left C. $42\,\text{N}$ to the right D. $0$, because two forces cancel

$30-12=18\,\text{N}$ in the direction of the larger force (right).

4. The resultant force on a $5.0\,\text{kg}$ trolley is $20\,\text{N}$. The acceleration is A. $0.25\,\text{m/s}^2$ B. $15\,\text{m/s}^2$ C. $4.0\,\text{m/s}^2$ D. $100\,\text{m/s}^2$

$a=F/m=20/5.0=4.0\,\text{m/s}^2$. D is $F \times m$.

5. A bag has mass $7.0\,\text{kg}$. Take $g=10\,\text{N/kg}$. Which statement is correct? A. Its weight on Earth is $7.0\,\text{N}$ B. Its weight on Earth is $70\,\text{N}$ and its mass on the Moon is still $7.0\,\text{kg}$ C. Its mass on the Moon is $70\,\text{kg}$ D. Weight and mass are the same quantity in different units

$W=mg=70\,\text{N}$ on Earth. Mass does not change on the Moon; weight does.

Quiz 4 of 5 · Specification 1.19–1.21

Stopping distance and terminal velocity

1. Stopping distance is A. thinking distance minus braking distance B. thinking distance plus braking distance C. only the distance while the brakes are on D. reaction time in seconds

1.19: stopping = thinking + braking. Thinking distance is a length, not a time.

2. Which factor increases thinking distance but not braking distance? A. an icy road B. worn tyres C. the driver drinking alcohol D. a heavier load in the boot

Alcohol increases reaction time, so thinking distance $= vt$ increases. A, B and D affect friction or mass, so braking distance.

3. A wet road increases stopping distance mainly because A. friction is reduced, so braking distance increases B. the driver’s reaction time becomes longer C. the mass of the car increases D. thinking distance doubles automatically

Road condition changes braking, not thinking, unless the driver also slows down.

4. A skydiver has just left the aircraft. Which statement is correct? A. Air resistance already equals weight B. There are no forces on the skydiver C. Weight is increasing as she falls D. Air resistance is small, so there is a downward resultant and she accelerates

At the start $v \approx 0$, so drag is small. Weight is constant. Forces exist from the first instant.

5. At terminal velocity A. air resistance equals weight, so acceleration is zero B. there are no forces acting C. the object is stationary in the air D. weight has become zero

Balanced forces, constant (usually large) speed downwards. Not “no forces” and not at rest.

Quiz 5 of 5 · Specification 1.22–1.24

Hooke’s law, the practical, and elastic behaviour

1. A spring is $12.0\,\text{cm}$ long with no load and $15.5\,\text{cm}$ with a load. The extension is A. $15.5\,\text{cm}$ B. $12.0\,\text{cm}$ C. $3.5\,\text{cm}$ D. $27.5\,\text{cm}$

Extension = stretched length − original length $= 15.5-12.0=3.5\,\text{cm}$.

2. Hooke’s law is associated with A. the initial linear region of a force–extension graph B. only the curved part of the graph after the spring has snapped C. any material, whether the graph is straight or not D. the area under a velocity–time graph

1.23: the initial linear region. A rubber band can be elastic without obeying Hooke’s law.

3. A force of $4.0\,\text{N}$ extends a spring by $8.0\,\text{cm}$ in the linear region. The spring constant $k$ is A. $0.50\,\text{N/m}$ B. $50\,\text{N/m}$ C. $32\,\text{N/m}$ D. $2.0\,\text{N/m}$

Convert first: $e=0.080\,\text{m}$. $k=F/e=4.0/0.080=50\,\text{N/m}$. A uses centimetres in the formula.

4. Elastic behaviour means a material A. stays permanently stretched after the load is removed B. has a force–extension graph that is always a straight line C. cannot change shape at all D. recovers its original shape after the deforming force is removed

This is the 1.24 specification sentence. A is plastic deformation. B is Hooke’s law, which is a different idea.

5. In the Hooke’s law practical, which statement about a rubber band is most accurate? A. You still measure force and extension, but the graph is usually non-linear B. A rubber band cannot be used because it has no extension C. The independent variable is the colour of the band D. Rubber never returns to its original length, so it cannot be elastic

1.22 names rubber bands as well as springs and wires. The method is the same; the graph usually curves. Rubber can still show elastic behaviour.