Exam Test2 PHY4A Spring 2015
Name________________________________
1) A pickup truck is moving at 25 m/s with a toolbox of mass m resting on the bed of the truck 2.5 m behind the cab.
Suddenly the brakes are applied, causing the toolbox to slide, and the truck comes to a stop in 4.7 s. The coefficient of
kinetic friction between the toolbox and the bed of the truck is 0.28. After the brakes are applied, what is the extra
displacement the toolbox travels before it strikes the cab?
2) A 600-kg car traveling at 24.5 m/s is going around a curve having a radius of 120 m that is banked at an angle of 20°.
(a) Is the curve properly banked for the car's speed?
(b) What is the minimum coefficient of static friction required between the road and the car's tires so the car does not
skid?
Draw a free body diagram for the car in question. Write Newton's 2 nd law showing all the forces in both x – and ydirection. (use the velocity square formula derived in the class to calculate the minimum coefficient of static friction )
3) A 50.0-kg box rests on a smooth horizontal surface. A constant force then acts on the box. It takes 6.9 seconds for the
car to travel 28 meters.
What is the force on the box ?
4) A 20.0-N box rests on a 50.0-N box on a perfectly smooth horizontal floor. When a horizontal 15.0-N pull to the right is
exerted on the lower box (see figure), both boxes move together. Find the magnitude and direction of the net external
force on the upper box.