11th grade forces and motion

Example

An object starts at 0 m/s and accelerates uniformly at 2.5 m/s² over 25 m. What is its final velocity, in m/s? (Give 1 decimal place.)

1. v² = 0² + 2 × 2.5 × 25 = 125
2. v = 11.18
3. So the answer is: 11.2 m/s

Answer: 11.2 m/s

Example

A 2 kg trolley moving at 4 m/s hits a stationary 4 kg trolley. They stick together. What is their velocity just after the collision, in m/s? (Give 2 decimal places.)

1. 2 × 4 = 8
2. v = 8 ÷ 6 = 1.333
3. So the answer is: 1.33 m/s

Answer: 1.33 m/s

Example

A 80 kg passenger moving at 15 m/s is brought to rest in 0.4 s by a seat belt and airbag. What is the average force on the passenger, in N?

1. Δp = 80 × 15 = 1200 kg m/s
2. F = 1200 ÷ 0.4 = 3000
3. So the answer is: 3000 N

Answer: 3000 N