constant acceleration and displacement are known?
A.B.C.D.A B C D
15.3 The city is trying to figure out how long the traffic light should stay yellow at an intersection. The speed limit on the road is
45.0 km/h and the intersection is 23.0 m wide. A car is traveling at the speed limit in the positive direction and can brake with
an acceleration of í5.20 m/s^2. (a) If the car is to stop on the white line, before entering the intersection, what is the minimum
distance from the line at which the driver must apply the brakes? (b) How long should the traffic light stay yellow so that if the
car is just closer than that minimum distance when the light turns yellow, it can safely cross the intersection without having to
speed up?
(a) m
(b) s
15.4 The brochure advertising a sports car states that the car can be moving at 100.0 km/h, and stop in 37.19 meters. What is its
average acceleration during a stop from that velocity? Express your answer in m/s^2. Consider the car's initial velocity to be a
positive quantity.
m/s^2
15.5 Engineers are designing a rescue vehicle to catch a runaway train. When the rescue vehicle is launched from a stationary
position, the train will be at a distance d meters away, moving at constant velocity v meters per second. The rescue vehicle
needs to reach the train in t seconds. Write an equation for the constant acceleration needed for the rescue vehicle in terms
of d,v, and t.
a = 2(vt + d)/t^2
a = (vtíd)/t
a = 2(dv + t)/vt^2
a = t(víd)
15.6 Two spacecraft are 13,500 m apart and moving directly toward each other. The first spacecraft has velocity 525 m/s and
accelerates at a constant í15.5 m/s^2. They want to dock, which means they have to arrive at the same position at the same
time with zero velocity. (a) What should the initial velocity of the second spacecraft be? (b) What should be its constant
acceleration?
(a) m/s
(b) m/s^2Section 18 - Free-fall acceleration
18.1 An elevator manufacturing company is stress-testing a new elevator in an airless test shaft. The elevator is traveling at an
unknown velocity when the cable snaps. The elevator falls 1.10 meters before hitting the bottom of the shaft. The elevator
was in free fall for 0.900 seconds. Determine its velocity when the cable snapped. As usual, up is the positive direction.m/s
18.2 A watermelon cannon fires a watermelon vertically up into the air at a velocity of + 9.50 m/s, starting from an initial position
1.20 meters above the ground. When the watermelon reaches the peak of its flight, what is (a) its velocity, (b) its acceleration,
(c) the elapsed time, and (d) its height above the ground?
(a) m/s
(b) m/s^2
(c) s
(d) m
18.3 A croissant is dropped from the top of the Eiffel Tower. The height of the tower is 300.5 meters (ignoring the antenna, and
this figure changes slightly with temperature). Ignoring air resistance, at what speed will the croissant be traveling when it hits
the ground?
m/s(^50) Copyright 2007 Kinetic Books Co. Chapter 2 Problems