Unit Revision PQ

Q and A

Q1

Q2

Q3

Q4

Q5

Q6

Q7

Q8

Q9

Q10

Q11

Q12

Q13

Q14

Q15

Q16

Q17

Q18

Q19

Q20• An aircraft is flying due north with a velocity of 200 m s−1. A side wind of velocity

50 m s−1 is blowing due east. What is the aircraft’s resultant velocity (give the magnitude and direction)?

Q21

• A cyclist is travelling at 15 m s−1. She brakes so that she doesn’t collide with the wall. Calculate the magnitude of her deceleration.

Q22• To get a rough value for g, a student dropped a stone from the top of a cliff . A

second student timed the stone’s fall using a stopwatch. Here are their results: estimated height of cliff = 30 m time of fall = 2.6 s Use the results to estimate a value for g.

Or alternatively

Q23• A cyclist of mass 60 kg rides a bicycle of mass 20 kg. When starting off, the cyclist

provides a force of 200 N. Calculate the initial acceleration.

Q24• A car of mass 500 kg is travelling at 20 m s−1. The driver sees a red traffic light

ahead, and slows to a halt in 10 s. Calculate the braking force provided by the car.

• Calculate the acceleration required. The car’s final velocity is 0 m s−1, so its change in velocity Δv = 0 − 20 = −20 m s−1

• Calculate the force, we use: F = ma = 500 × −2 = −1000 N So the brakes must provide a force of 1000 N. (The minus sign shows a force decreasing the velocity of the car.)

Q25• A boy of mass 40 kg is on a waterslide which slopes at 30° to the horizontal. The

frictional force up the slope is 120 N. Calculate the boy’s acceleration down the slope. Take the acceleration of free fall g to be 9.81 m s−2.

Boy’s weight W = 40 × 9.81 = 392

N the frictional force up the slope F = 120 N

Contact force N at 90° to the slope

Component of W down the slope = 392 × cos 60° = 196

N component of F down the slope = −120 N (negative because F is directed up the slope)

Component of N down the slope = 0 (because it is at 90° to the slope)

It is convenient that N has no component down the slope, since we do not know the value of N.

Calculate the resultant force on the boy: resultant force = 196 − 120 = 76 N

Calculate his acceleration:

acceleration = resultant force mass =

76 40 = 1.9 ms−2

Q26• A ship is pulled at a constant speed by two small boats, A and B. The engine of the

ship does not produce any force.

Q27• A block of mass 1.5 kg is at rest on a rough surface which is inclined at 20° to the

horizontal as shown.

Q28• A man pulls a box along horizontal ground using a rope. The force provided by the

rope is 200 N, at an angle of 30° to the horizontal. Calculate the work done if the box moves 5.0 m along the ground.

• horizontal component of force = 200 cos 30° ≈ 173 N

• work done = force × distance moved = 173 × 5.0 = 865 J

Q29• The crane shown lifts its 500 N load to the top of the building from A to B.

Distances are as shown on the diagram. Calculate how much work is done by the crane.

Q30• Diagram shows the forces acting on a box which is being pushed up a slope.

Calculate the work done by each force if the box moves 0.50 m up the slope.

Q31• A 120 kg crate is dragged along the horizontal ground by a 200 N force acting at an

angle of 30° to the horizontal, as shown in Figure 5.20. The crate moves along the surface with a constant velocity of 0.5 m s−1. The 200 N force is applied for a time of 16 s.

Q32

Q33• A sprint cyclist starts from rest and accelerates at 1 m/s2 for 20 seconds. He then

travels at a constant speed for 1 minute and finally decelerates at 2 m/s2 until he stops. Find his maximum speed in km/h and the total distance covered in metres.

Q34• A ball is projected vertically upwards with an initial velocity of 30 m/s. Find a its

maximum height and b the time taken to return to its starting point. Neglect air resistance and take g = 10 m/s2.

Q35• A block of mass 2 kg has a constant velocity when it is pushed along a table by a

force of 5 N. When the push is increased to 9 N what is a the resultant force, b the acceleration?

Q36• Use the direction conventions to determine the perpendicular components of a

235 N force acting on a bike at a direction of 17.0° north of west.

Q37

Q38• A golf ball is dropped onto a concrete floor and strikes the floor at 5.0 m s–1.

It then rebounds at 5.0 m s–1. The contact with the floor lasts for 25 ms.

Q39• A construction worker accidentally knocks a brick from a building so that it falls

vertically a distance of 50 m to the ground. Use g = –9.8 m s–2 and ignore air resistance.

• How long does the brick take to fall halfway, to 25 m?

Q40• A 2 tonne truck travelling at 100 km h–1 slows to 80 km h–1 before turning a

corner.

• Calculate the work done by the brakes to make this change. Give answers to two significant figures.

Q40 continued

• If it takes 50 m for this deceleration to take place, calculate the average force applied by the truck’s brakes.