Kinesiology and Biomechanics Questions and Answers

Answer: D

The biceps femoris is a major muscle of the posterior side of the thigh.

The biceps femoris is the lateral member of the hamstring group, together with the semitendinosus and semimembranosus, at the back of the thigh. It flexes the knee and extends the hip, and is often strained in sprinting.

The anterior upper arm holds the biceps brachii (not biceps femoris), the posterior upper arm holds the triceps brachii, and the front of the thigh holds the quadriceps femoris group.

Answer: C

Kyphosis is a deformity at the thoracic region.

Kyphosis is an exaggerated backward (convex) curve of the upper back, giving a rounded back or hunchback. The thoracic spine is normally slightly convex backwards, and kyphosis is an excess of that curve, often linked to poor posture, weak back muscles or osteoporosis.

An exaggerated inward curve of the lumbar region is lordosis, and a sideways curve is scoliosis. The cervical and coccygeal regions are not where kyphosis is defined.

Answer: B

Stability is inversely proportional to the height of the body, that is, the height of its centre of gravity.

The higher the centre of gravity above the base of support, the smaller the tilt needed to carry the line of gravity outside the base, so the less stable the body. That is why athletes crouch and lower their centre of gravity to resist being pushed over.

The other factors work the other way: stability increases with body weight, with the size of the base of support, and with the distance of the line of gravity from the edge of the base. All three are directly, not inversely, related to stability.

Answer: C

Inertia causes an object to resist any change in the state of motion.

Inertia is the property expressed in Newton's first law: a body stays at rest or keeps moving at constant velocity unless an external force acts on it. It resists starting, stopping and changing direction alike, and the greater the mass, the greater the inertia.

Inertia does not by itself increase or decrease speed; each of those is a change of motion that requires a force. Slowing down because of friction is the effect of an external force, not of inertia.

Answer: D

This is active insufficiency.

A two-joint (biarticular) muscle crosses two joints. When it contracts to move both joints at once, it shortens so far that its fibres can no longer develop enough tension to complete the full range of motion at both. The hamstrings, for example, cannot fully flex the knee while the hip is fully extended.

Passive insufficiency is the opposite case: the two-joint muscle is stretched over both joints and cannot lengthen enough to allow full range at both, as when the hamstrings limit hip flexion with the knee straight. Biarticulate and multiarticulate only describe how many joints a muscle crosses.

Answer: D

The resultant is 2 N towards the east.

Forces along the same line add with their signs. Taking east as positive:

\[ \begin{aligned} F &= 10 + 18 - 26 \\ &= 28 - 26 = +2\ \text{N} \end{aligned} \]

The positive sign means the resultant acts towards the east.

54 N is what you get by adding all three magnitudes as if they acted in the same direction. 12 N and 24 N do not follow from any correct combination of the three forces.

Answer: C

The product is angular momentum.

Angular momentum is the rotational counterpart of linear momentum (mass × velocity):

\[ L = I\omega \]

where I is the moment of inertia and ω the angular velocity. In flight it is conserved, which is why a diver or gymnast who tucks (smaller I) spins faster.

Angular velocity is one of the two factors, not the product. Angular acceleration is the rate of change of angular velocity, and 'angular projection' is not a standard mechanical quantity.

Answer: B

Angular velocity increases by decreasing the radius.

Linear velocity at the end of a rotating radius is v = rω, so

\[ \omega = \frac{v}{r} \]

With v held constant, a smaller radius gives a larger angular velocity. A gymnast who pulls the body in towards the axis of rotation, for example by tucking, rotates faster.

Increasing the radius lowers ω, so options A and C are wrong (C also changes the velocity, which the question holds constant), and with no change in radius ω stays the same.

Answer: C

It is the Magnus effect.

A spinning ball drags a thin layer of air round with it. On one side the spin adds to the airflow speed and on the other it opposes it, so the pressure is lower on the faster side, and the ball is pushed towards it. This sideways force bends the flight of a swinging free kick in football, topspin and slice in tennis, and the hook or slice of a golf ball.

Buoyancy is the upward force of a fluid on an immersed body. 'Physical effect' and 'magnitude effect' are not names for the curve of a spinning ball.

Answer: A

The code is a-2, b-3, c-4, d-1.

• Kyphosis is an exaggerated backward curve of the thoracic region (round back).
• Effleurage, the stroking movement, is a technique of massage.
• Lordosis is an exaggerated forward curve of the lumbar region (hollow back).
• A diarthrosis is a synovial joint, freely movable.

Option C swaps lordosis and diarthrosis, and options B and D misplace kyphosis, so only A is correct.