NAME: ____________________________ DATE: __________________________
EXAM 2
Show ALL Work. (No work = no points)
Answer the following questions by justifying your answer.
1. If the acceleration of an object is zero, are no forces acting on it? Explain.
2. When a golf ball is dropped to the pavement, it bounces back up. (A) is a force needed
to make it bounce back up? (B) if so, what exerts the force?
3. A father and his young daughter are ice skating. They face each other at rest and push
each other, moving in opposite directions. Which one has the greater final speed?
4. Suppose that you are standing on a cardboard carton that just barely supports you.
What would happen to it if you jumped up into the air? (A) collapse; (B) be unaffected;
(C) spring upward a bit; (D) move sideways.
5. When you stand still on the ground, how large a force does the ground exert on you?
Why doesn’t this force make you rise up into the air?
6. Mary exerts an upward force of 40 N to hold a bag of groceries. Describe the “reaction”
force (Newton’s third law) by stating (a) its magnitude, (b) its direction, (c) on what
object it is exerted, and (d) by what object it is exerted.
7. A window washer pulled herself upward using the bucket pulley apparatus shown in the
figure.
(A) How hard must she pull downward to raise herself slowly at constant speed? (B) If she
increases this force by 20%, what will her acceleration be? The mass of the person plus
the bucket is 75 kg.
8. At the instant a race began, a 75-kg sprinter exerted a force of 760 N on the starting
block at a 23° angle with respect to the ground. (A) What was the horizontal
acceleration of the sprinter? (B) If the force was exerted for 0.36 s, with what speed did
the sprinter leave the starting block?
9. Uphill escape ramps are sometimes provided to the side of steep downhill highways for
trucks with overheated brakes. For a simple 13° upward ramp, what length would be
needed for a runway truck traveling 180 km/h?
10. A 37-kg chandelier hangs from a ceiling on a vertical 6.0 m long wire. (A) What
horizontal force would be necessary to displace its position 0.25 m to one side? (B)
What will be the tension in the wire?
11. The block shown in the figure has mass m = 9.0 kg and lies on a fixed smooth frictionless
plane tilted at an angle θ = 28.0° to the horizontal. (Α) Determine the acceleration of the
block as it slides down the plane. (Β) If the block starts from rest 10.0 m up the plane
from its base, what will be the blocks speed when it reaches the bottom of the incline?
12. A block is given an initial speed of 4.5 m/s up the 28° plane shown in the previous figure
from the previous problem. (A) How far up the plane will it go? (B) How much time
elapses before it returns to its starting point? Ignore friction.
13. An object is hanging by a string from your rearview mirror. While you are accelerating at
a constant rate from rest to 33 m/s in 7.0 seconds, what angle does the string make with
the vertical?
14. A car rounds a curve at a steady 50 km/h. If it rounds the same curve at a steady 70 km/h,
will its acceleration be any different? Explain.
15. A 1200 kg car is driving toward the north along a straight road at a speed of 24.0 m/s.
The driver applies the brakes and the car comes to a rest in a distance of 180 m. What is
the constant force applied to the car to bring it to rest?
16. A 2-kg ball is moving with a constant speed of 5 m/s in a horizontal circle whose radius is
50 cm. What is the magnitude of the net force on the ball?
17. A 5.00 kg box slides 4.00 m across the floor before coming to rest. What is the
coefficient of kinetic friction between the floor and the box if the box had an initial speed
of 4.00 m/s?
18. A child stands on a playground merry-go-round a distance of 1.50 m from the rotational
axis. The coefficient of static friction between the child’s shoes and the surface is 0.700.
Assuming the g = 9.81 m/s , what is the maximum revolutions per second the merry-go-
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round can do for which the child will not start to slide?
19. A car drives over a hilltop that has a radius of curvature 120 m at the top of the hill. At
what speed would the car be traveling when its tires just barely lose contact with the
road when the car is at the top of the hill?
20. A 600-kg car is going around a curve with a radius of 120 m that is banked at an angle of
20 degrees with a speed of 24.5 m/s. What is the minimum coefficient of static friction
required for the car not to skid?
