WHAT IS NASA PHYSICS?
Forces and Motion
Conservation of Momentum & Energy
Temperature and Heat
Anticipation Guide 7
Intro to Modern Physics
The Ultraviolet Catastrophe
The Photoelectric Effect
Special Relativity (SR)
Distance and Time
May the Forces be with You
Modern Physics Notebook
Assessment Problems 7
Forces and Motion
Speed and Velocity
Newton's Laws of Motion
1. A car travels for 2 hours at 50 miles/hour and another hour at 100 miles/hour. What is the car’s average speed for the trip?
Answer: Determine how far the car traveled in each part of the trip.
(50 mi/hr) 2 hrs = 100 miles
(100 mi/hr) 1 hr = 100 miles
The total distance traveled is 200 miles. Then v = d/t = 200 mi/3 hr = 67 mi/hr.
2. Car A accelerates at a rate a for a time of t seconds. Car B undergoes acceleration at a rate of 2a for a time of t/2 seconds. Which car traveled the greater distance? Assume both cars start from rest.
Answer: Car A travels twice as far as car B. As an example, let car A accelerate at 1 m/s2 for 10 seconds.
Then dA = ½at2 = ½(1 m/s2)(10 s)2 = 50 m
The distance traveled by car B would then be dB = ½(2 m/s2)(5 s)2 = 25 m
3. A student throws a rock horizontally from the top of a cliff into a lake at the same instant a second student drops a rock vertically downward. If the rocks are released at the same instant and fall the same vertical height, which rock hits the water first?
Answer: Both rocks will strike the water at the same time.
The horizontal motion of the rock is independent of the vertical displacement.
4. How would your answer change if the initial speed of the rock thrown horizontally was doubled?
Answer: Again, both rocks will strike the water at the same time.
The rock thrown horizontally will land twice as far from the base of the cliff.