8th grade forces and motion

Example

A force of 5 N is applied 1.5 m from a pivot, at right angles. What is the moment, in N m?

1. 5 × 1.5 = 7.5
2. So the answer is: 7.5 N m

Answer: 7.5 Nm

Example

Distance (m) against time (s) for a walk: (0, 0), A (10, 20), B (30, 20), C (50, 140). What was the average speed for the whole walk, in m/s? Give 2 decimal places.

1. 140 ÷ 50 = 2.8
2. So the answer is: 2.8 m/s

Answer: 2.8 m/s

Example

A passenger lurches forward when a bus brakes suddenly. Which law explains this?

1. An object keeps moving at the same velocity unless a resultant force acts (inertia).
2. So the answer is: Newton's first law (inertia)

Answer: Newton's first law (inertia)

Example

A car's engine provides a driving force of 2000 N forwards. Air resistance is 300 N and friction is 150 N, both backwards. What is the resultant force, in N?

1. 300 + 150 = 450
2. 2000 − 450 = 1550
3. The resultant acts forwards, so the car speeds up.
4. So the answer is: 1550 N

Answer: 1550 N

Example

Is distance a scalar or a vector quantity?

1. Scalars have size (magnitude) only.
2. So the answer is: scalar (size only)

Answer: scalar (size only)