PRACTICE PROBLEM # 1
1. A car going 15 m/s is brought to rest in a distance of 2.0 m as it strikes a pile
of dirt. How large an average force is exerted by seatbelts on a 90-kg
passenger as the car is stopped?
2. Figure 6-3 shows a bead sliding on a wire. If friction forces are negligible and
the bead has a speed of 200 cm/s at A, what will be its speed (a) at point B?
(b) At point C?
3. A spring loaded barrier can be used to stop a runaway vehicle. What spring
constant would be required if a vehicle of mass 2200 kg moving at 3.0 m/s is
to be stopped in a distance of 80 cm?
4. A Jaguar car of mass 2M is racing a small Austin Healy sports car of mass M.
Initially the Jaguar has half the kinetic energy of the Austin Healy, but when
the Jaguar then speeds up by 10 m/s, the two vehicles have the same kinetic
energy. What were the initial speeds of the two cars?
5. Combustion of 1gal of gasoline yields 1.3 x10 8J. Consider a car that can travel
28mi/gal at a speed of 90km/h. Of the energy obtained from burning the
gasoline, 25 percent goes into driving the car, with the rest dissipated as
heat. What is the average frictional force acting on the car?
6. An advertisement claims that a certain 1200-kg car can accelerate from rest
to a speed of 25 m/s in a time of 8.0 s. What average power must the motor
produce to cause this acceleration? Ignore friction losses.
PRACTICE PROBLEM # 2
1. A 2.0-kg brick is moving at a speed of 6.0 m/s. How large a force F is needed
to stop the brick in a time of 7.0 x 10-4 s?
2. A football running back of mass 90 kg moving 5 m/s is tackled head on by a
linebacker of mass 120 kg running 4 m/s. They stick together. Who knocks
whom back, and how fast are they moving just after the tackle?
3. The nucleus of an atom has a mass of 3.80 x 10 kg and is at rest. The nucleus
is radioactive and suddenly ejects a particle of mass 6.6 x 1027 kg and speed
1.5 x 10' m/s. Find the recoil speed of the nucleus that is left behind.
4. A 0.25-kg ball moving in the + x-direction at 13 m/s is hit by a bat. Its final
velocity is 19 m/s in the - x-direction. The bat acts on the ball for 0.010 s. Find
the average force F exerted on the ball by the bat.
5. A 7500-kg truck traveling at 5.0 m/s east collides with a 1500-kg car moving
at 20 m/s in a direction 30° south of west. After collision, the two vehicles
remain tangled together. With what speed and in what direction does the
wreckage begin to move?
