Name: ______
Practice – 2.7Falling Objects
1. A stone is dropped from the top of a cliff. It hits the ground below after 3.25 s. How high is the cliff?
2. A light plane must reach a speed of 33 m/s for takeoff. If it can accelerate at 0.50 g, how long of a runway does it need?
3. A world-class sprinter can burst out of the blocks to essentially top speed (of 11.5 m/s) in the first 15.0 m of the race.
A. What is the average acceleration of this sprinter?
B. How long does it take her to reach that speed?
4. Superman jumps straight down from the top of the Empire State Building (380 m high). What is his velocity just before “landing”?
5. A ballplayer catches a ball 3.0 s after throwing it vertically upward.
A. With what speed did he throw it?
B. What height did it reach?
6. In coming to a stop, a car leaves skid marks 92 m long on the highway. Assuming a deceleration of 7.00 m/s2, estimate the speed of the car just before braking?
7. A car traveling 85 km/h strikes a tree. The front end of the car compresses and the driver comes to rest after traveling a distance of 0.80 m. What was the average acceleration of the driver during the collision? Express the answer in terms of g.
8. A helicopter is ascending vertically with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped. How much time does it take the package to hit the ground?
9. A stone is dropped from a bridge and hits the water 2.5 seconds later.
A. How far did it fall?
B. What was its velocity just before hitting the water?
10. A ball is thrown vertically with a velocity of +25.0 m/s.
A. How long does it take the ball to reach its highest point?
B. What is its velocity at its highest point?
C. What is its acceleration at its highest point?
11.* A falling stone takes 0.28 s to travel past a window 2.2 m tall. From what height above the top of the window was the stone released?
Solutions:
1. 51.8 m
2. 110 m
3. A. 4.41 m/s2 B. 2.61 s
4. -86.3 m/s
5. A. 14.7 m/s B. 11.0 m
6. 36 m/s
7. 36 g
8. 5.61 s
9. A. -31 m B. -25 m/s
10. A. 2.55 s B. 0 m/s C. -9.80 m/s2
11.* 2.1 m