PRACTICE IT Use the worked example above to help you solve this problem. An pickup truck with mass 1.85 x 10³ kg is traveling eastbound at +14.3 m/s, while a compact car with mass 8.61 x 102 kg is traveling westbound at -14.3 m/s. (See figure.) The vehicles collide head-on, becoming entangled. (a) Find the speed of the entangled vehicles after the collision. m/s (b) Find the change in the velocity of each vehicle. m/s Av truck Av car m/s (c) Find the change in the kinetic energy of the system consisting of both vehicles. J

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STRATEGY The total momentum of the vehicles before the
collision, Pi, equals the total momentum of the vehicles after the collision, pf, if we ignore friction and
assume the two vehicles form an isolated system. (This is called the "impulse approximation.") Solve the
momentum conservation equation for the final velocity of the entangled vehicles. Once the velocities are
in hand, the other parts can be solved by substitution.
SOLUTION
(A) Find the final speed after collision.
Let m₁ and V₁¡ represent the mass
and initial velocity of the pickup truck,
while m₂ and V₂¡ pertain to the
compact. Apply conservation of
momentum.
Substitute the values and solve for the
final velocity, Vf.
Pi Pf
m₁v₁; + m₂V₂i = (m₁ + m₂) vf
Vf
(B) Find the change in velocity for each vehicle.
Change in velocity of the pickup truck.
Change in velocity of the compact car.
Calculate the final kinetic energy of the
system and the change in kinetic
energy, AKE.
(1.80 x 10³ kg)(15.0 m/s) + (9.00 × 10² kg)(-15.0 m/s)
(1.80 x 10³ kg + 9.00 × 10² kg)vf
+5.00 m/s
=
=
(C) Find the change in kinetic energy of the system.
Calculate the initial kinetic energy of
the system.
b
AV₁ = Vf - V₁i
AV₂ = VfV₂i = 5.00 m/s - (-15.0 m/s) = 20.0 m/s
KE₁ = 1/2m₁v₁/² + 1/2m₂v₂2²2
=
AKE
= 5.00 m/s 15.0 m/s =
=
(1.80 × 10³ kg)(15.0 m/s)²
+ (9.00 × 10² kg)(-15.0 m/s)²
= 3.04 x 105 J
VE
KE₁ = 1/(m₂ + m₂) v²
=
(1.80 × 10³ kg + 9.00 × 10² kg)(5.00 m/s)²
= 3.38 x 104 J
VE
-10.0 m/s
2.70 x 105 1
Transcribed Image Text:STRATEGY The total momentum of the vehicles before the collision, Pi, equals the total momentum of the vehicles after the collision, pf, if we ignore friction and assume the two vehicles form an isolated system. (This is called the "impulse approximation.") Solve the momentum conservation equation for the final velocity of the entangled vehicles. Once the velocities are in hand, the other parts can be solved by substitution. SOLUTION (A) Find the final speed after collision. Let m₁ and V₁¡ represent the mass and initial velocity of the pickup truck, while m₂ and V₂¡ pertain to the compact. Apply conservation of momentum. Substitute the values and solve for the final velocity, Vf. Pi Pf m₁v₁; + m₂V₂i = (m₁ + m₂) vf Vf (B) Find the change in velocity for each vehicle. Change in velocity of the pickup truck. Change in velocity of the compact car. Calculate the final kinetic energy of the system and the change in kinetic energy, AKE. (1.80 x 10³ kg)(15.0 m/s) + (9.00 × 10² kg)(-15.0 m/s) (1.80 x 10³ kg + 9.00 × 10² kg)vf +5.00 m/s = = (C) Find the change in kinetic energy of the system. Calculate the initial kinetic energy of the system. b AV₁ = Vf - V₁i AV₂ = VfV₂i = 5.00 m/s - (-15.0 m/s) = 20.0 m/s KE₁ = 1/2m₁v₁/² + 1/2m₂v₂2²2 = AKE = 5.00 m/s 15.0 m/s = = (1.80 × 10³ kg)(15.0 m/s)² + (9.00 × 10² kg)(-15.0 m/s)² = 3.04 x 105 J VE KE₁ = 1/(m₂ + m₂) v² = (1.80 × 10³ kg + 9.00 × 10² kg)(5.00 m/s)² = 3.38 x 104 J VE -10.0 m/s 2.70 x 105 1
PRACTICE IT
Use the worked example above to help you solve this problem. An pickup truck with mass 1.85 x 10³ kg is
traveling eastbound at +14.3 m/s, while a compact car with mass 8.61 x 10² kg is traveling westbound at
-14.3 m/s. (See figure.) The vehicles collide head-on, becoming entangled.
(a) Find the speed of the entangled vehicles after the collision.
m/s
(b) Find the change in the velocity of each vehicle.
Av truck
Av car
=
(c) Find the change in the kinetic energy of the system consisting of both vehicles.
J
m/s
m/s
EXERCISE
HINTS: GETTING STARTED I I'M STUCK!
Use the values from PRACTICE IT to help you work this exercise. Suppose the same two vehicles are both
traveling eastward, the compact car leading the pickup truck. The driver of the compact car slams on the
brakes suddenly, slowing the vehicle to 6.09 m/s. If the pickup truck traveling at 17.7 m/s crashes into
the compact car, find the following.
(a) the speed of the system right after the collision, assuming the two vehicles become entangled
m/s
(b) the change in velocity for both vehicles
Avtruck
m/s
m/s
Av car
=
=
(c) the change in kinetic energy of the system, from the instant before impact (when the compact
car is traveling at 6.09 m/s) to the instant right after the collision
AKE =
J
Transcribed Image Text:PRACTICE IT Use the worked example above to help you solve this problem. An pickup truck with mass 1.85 x 10³ kg is traveling eastbound at +14.3 m/s, while a compact car with mass 8.61 x 10² kg is traveling westbound at -14.3 m/s. (See figure.) The vehicles collide head-on, becoming entangled. (a) Find the speed of the entangled vehicles after the collision. m/s (b) Find the change in the velocity of each vehicle. Av truck Av car = (c) Find the change in the kinetic energy of the system consisting of both vehicles. J m/s m/s EXERCISE HINTS: GETTING STARTED I I'M STUCK! Use the values from PRACTICE IT to help you work this exercise. Suppose the same two vehicles are both traveling eastward, the compact car leading the pickup truck. The driver of the compact car slams on the brakes suddenly, slowing the vehicle to 6.09 m/s. If the pickup truck traveling at 17.7 m/s crashes into the compact car, find the following. (a) the speed of the system right after the collision, assuming the two vehicles become entangled m/s (b) the change in velocity for both vehicles Avtruck m/s m/s Av car = = (c) the change in kinetic energy of the system, from the instant before impact (when the compact car is traveling at 6.09 m/s) to the instant right after the collision AKE = J
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