P5: Quiz 14 – Answers

2)

a)

i) The object will remain stationary

ii) The object will continue moving with a constant velocity

b) It can:

- start moving
- stop moving
- speed up
- slow down
- change direction.

3)

a) The resultant force is 0 N

b) The ball will remain stationary

4)

a) force = mass x acceleration

F = ma

Force/ resultant force is measured in newtons (N), mass is measured in kilograms (kg) and acceleration is measured in metres per second squared (m/s^{2})

b) Directly proportional

b) Inversely proportional

5) 4.5 N

6) 3,000 N

7) 0.72 N

8) 3 m/s^{2}

9) 6 kg

10)

a) 800 N (to the right)

b) 0.5 m/s^{2} (to the right)

11)

a) 3.6 m/s^{2} (or -3.6 m/s^{2})

b) 6,120 N

12)

a) 1.375 m/s^{2}

b) 261.25 N

13)

a) The law of inertia is also called Newton’s first law, which is that an object’s motion will remain the same unless a resultant force acts on the object

b) Inertia mass is a measure of how difficult it is to change the velocity of an object. The formula for inertia mass is m = f ÷ a or m = f/a

**Questions**

1) Define resultant force.

2)

a)

i) If the resultant force acting on a stationary object is 0, what will happen to the object?

ii) If the resultant force acting on a moving object is 0, what will happen to the object?

b) If the resultant force acting on an object is non-zero, what are the 5 different things that can happen to the object?

3) The ball below is stationary and there are two forces acting on the ball.

a) Find the resultant force acting on the ball.

b) Will the ball remain stationary or will the ball start to move?

4)

a) What is the equation for Newton’s second law? Include the units for the variables in your formula.

b) How would you describe the relationship between resultant force and acceleration; directly proportional or inversely proportional?

c) How would you describe the relationship between acceleration and mass; directly proportional or inversely proportional?

5) A ball has a mass of 1.5 kg and an acceleration of 3 m/s^{2}. Find the resultant force acting on the ball.

6) A car has a mass of 1,500 kg and is accelerating at 2 m/s^{2}. Find the resultant force acting on the car.

7) An object has a mass of 600 grams. A force causes the object to accelerate at a rate of 1.2 m/s^{2}. Calculate the size of the resultant force.

8) A ball has a mass of 6 kg. Find the acceleration of the ball when there is a resultant force of 18 newtons acting on the ball.

9) A force of 27 newtons causes an object to accelerate at a rate of 4.5 m/s^{2}. Find the mass of the object.

10) A car that has a mass of 1,600 kg is travelling towards the right. It has a driving force of 5,000 newtons, and the total resistive forces are 4,200 newtons. The diagram below shows these forces acting on the car.

b) Calculate the acceleration of the car.

*The next two questions require us to use the acceleration formulas that we looked at in the acceleration section.*

11) A car is approaching a set of traffic lights at a velocity of 18 m/s. The lights turn red and the car decelerates and comes to rest. It takes the car 5 seconds to stop. The car has a mass of 1,700 kg.

a) Work out the deceleration rate.

b) Calculate the (braking) force applied by the brakes to cause the car to stop.

12) A motorbike accelerates from a velocity of 6 m/s to a velocity of 16 m/s. The motorbike covers 80 metres whilst accelerating. The mass of the motorbike is 190 kg.

a) Work out the acceleration rate of the motorbike.

b) Calculate the resultant force causing the motorbike to accelerate.

13)

a) What does inertia mean?

b) What is inertia mass? Give the formula/ equation for inertia mass.