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Forces Practice Problems

1. If an object remains at rest, there must be no net force acting on it. Is this statement
correct? Explain.
2. The tendency of an object to maintain its state of motion is called a) Newton's first law b)
inertia c) mass
3. If an object is traveling at constant velocity, a) there must be a force in the direction of the
velocity, b)there must be no force in the direction of the velocity, c) there must be no net
4. If the net force on an object is zero, the object must a) be at rest b)be in motion c) have
zero acceleration d) none of these.
5. Consider a child holding a helium filled balloon in a closed car at rest. What would the child
observe when the car (a) accelerates from rest and (b) brakes to a stop? (The balloon does not
touch the roof of the car.)
6. When a horizontal force of 300 N is applied to a 75 kg box, the box slides on a level floor,
opposed by a force of kinetic friction of 120 N. What is the acceleration of the box?
2.40 m/s2
7. In an emergency stop to avoid an accident, a shoulder-strap seat belt holds a 60 kg
passenger firmly in place. If the car was initially traveling at 90 km/h and came to a stop in
5.5 s along a straight, level road, what was the average force applied to the passenger by the
2.7 x 102 N
8. In serving, a tennis player accelerates a 56g tennis ball from rest to a speed of 35 m/s.
Assuming the acceleration is uniform when the racquet applies a force over a distance of 0.50
m, what is the magnitude of the force exerted on the ball?
69 N
9. The force pair of Newton's third law a) consists of forces that are always opposite but not
always equal b)always cancel each other out when the second law is applied to a body, c)
always act on the same object d)consists of forces that are equal and opposite but act on
different objects
10. In the pairs competition of Olympic figure skating, a male skate with a mass of 60 kg and a
female skater who has a mass 45 kg, causing her to accelerate at a rate of 2.0 m/s 2. At what
0.77 m/s2
11. A 75 kg person is standing on a scale in an elevator. What is the reading of the scale in
newtons if the elevator is (a) at rest, (b) moving with constant velocity, (c) accelerating up at
2.0 m/s2 ?
c. 885 N
12. Two boats pull a 75.0 kg water skier as illustrated below. a)If each boat pulls with a force
of 600N and the skier travels with a constant velocity, what is the magnitude of the frictional
force between the water and the skis? b) Assuming the frictional force remains constant, if
each boat pulls with a force of 700N, what is the magnitude of the acceleration of the skier?
a) 849 N b) 1.88 m/s2


13. An Olympic Skier coasts down a slope with an angle of inclination of 37. a) Neglecting
friction, what is the acceleration of the skier? b) If the skier has a speed of 5.0 m/s at the top
of the slope, what is his speed when he reaches the bottom of the 35 m long slope?
a) 5.9 m/s2 b) 21 m/s
14. A car is coasting (engine off) up a 30 grade incline. If the speed of the car is 25 m/s at
the bottom of the grade, what is the distance traveled by the car before coming to a rest?
64 m
15. A 50 kg gymnast hangs vertically from a pair of parallel rings. a) If the ropes supporting
the rings are attached to the ceiling directly above, what is the tension in each rope? b)If the
ropes are supported so that they make an angle of 45 with the ceiling, what is the tension in
each rope?
a)2.5 x102 N b) 3.5 x 102N
16. Two masses of 0.25 kg and 0.20 kg are suspended in the air with a massless rope and a
frictionless and massless pulley. Under ideal conditions , what will be the acceleration of the
smaller mass?
1.1 m/s2 up
17. In the ideal setup below (massless rope and no friction) What is the mass of m 2 if both
masses are at rest? How about if both are moving at constant velocity?
1.2 kg ; 1.2 kg
m1 = 3.0 kg
18. A hockey player hits a puck with her stick, giving the puck an initial speed of 5.0 m/s. If
the puck slows uniformily and comes to rest in a distance of 20 m, what is the coefficient of
kinetic friction between the ice and the puck? 0.064
19. While being unloaded from a moving truck, a 10 kg suitcase is placed on a flat ramp
inclined at 37. When released from rest, the suitcase accelerates down the ramp at 0.15
m/s2. What is the coefficient of kinetic friction between the suitcase and the ramp?
20. A 0.45 kg shuffleboard puck is given an initial speed of 4.5 m/s down the flat playing
surface. If the coefficient of the friction between the puck and the surface is 0.20, how far will
the puck slide before coming to rest?
5.2 m