# Physics 160 Biomechanics Chapter 3 problems answer key

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```					Physics 160 Biomechanics Chapter 3

1. Inertia is

a. something that causes or tends to cause a change in the motion
of an object or body
b. the space a body occupies
*c. a body's resistance to having its state of motion changed
d. the amount of matter an object contains
e. the effect of a force

2. If a scale shows that an individual has a mass of 68 kg, what is that
individual's weight? (Be as precise as possible.)

a. 68 kg
*b. 667 N
c. either a or b
d. neither a nor b

3. A free-body diagram displays

a. the weight distribution of a body on a surface
b. the pressure distribution of a body on a surface
c. the mass distribution of a body
*d. the forces acting on a body
e. none of the above

4. In which of the following situations do the forces on the body sum to
zero?

a. vertical forces of -80 N, +30 N, and +40 N
*b. horizontal forces of -50 N, -20 N, +40 N, and +30 N
c. neither a nor b
d. both a and b

5. The force that acts perpendicular to an object in contact with a
surface is called

a. a shear force
*b. a normal force
c. an internal force
d. a colinear force
e. a resolved force

6. When drawing a sketch of a dancer pushing off in a jump, which of the
following is NOT a force to be considered?
a. the dancer's weight
b. the push of the floor on the dancer's foot
*c. the speed of the dancer across the floor
d. the friction of the floor on the dancer's shoe

7. How much does a 115 kg barbell weigh in newtons?

1128 newtons

8. How does mass differ from weight?

a. Mass is a force and weight is the quantity of matter in a body.
*b. Weight is a force and mass is the quantity of matter in a
body.
c. Mass refers to density and weight refers to volume.
d. Weight refers to density and mass refers to volume.
e. Mass and weight are the same.

9. To fully define a vector quantity, you must specify

a. length and magnitude
b. length and area
c. area and direction
*d. direction and magnitude
e. none of the above

10. Which of the following, when present, is NOT an external force
applied to a runner?

a. gravitational force
b. weight
c. friction
*d. muscle force
e. All of the above are external forces.

11. Which of the following is not a force?

a. friction
*b. mass
c. weight
d. gravity

12. An unbalanced horizontal force of 200 N is applied to a wrestler of
mass 100 kg. The horizontal acceleration of the wrestler will be

a. 200 m/s/s
b. 100 m/s/s
*c. 2 m/s/s
d. 1 m/s/s

13. Gravity can be defined as

*a. the force with which the earth pulls on an object's mass
b. the amount of force acting over a given area
c. an object's mass per unit volume
d. an object's weight per unit volume
e. a buoyant force

14. If the resultant acceleration of a 2 kg ball is 5.0 m/s/s
horizontally, the resultant force must be

a. 0.4 N
b. 2.5 N
c. 7.0 N
*d. 10.0 N