Exam 2: Kinetics of Linear Motion

A cricketer (mass = 85 kg) leaps up to catch a ball (mass = 0.16 kg) travelling to the boundary at 27 m/s. Assuming the catch is successful what is the horizontal momentum of the player and ball immediately after the catch is taken, before the player lands on the ground?

The force from gravity does not affect the horizontal motion of an object in flight.

Impulse can be increased by which of the following?

The force that is exerted by a muscle to pull on a tendon and bone to flex a joint (e.g. when bringing the forearm closer to the upper arm during a bicep curl movement) would be classed as an 'attractive force'.

The attractive force between Earth and a large boulder will be greater than the attractive force between the Earth and a golf ball. However, the acceleration during free-fall of the golf ball and the boulder will still remain the same if they were dropped from the same height.

Gravity affects what components of projectile motion?

An athlete performing a javelin throw may adjust their technique throughout the run-up and throw in order to increase the time of force application on the javelin. This should in turn increase the release velocity of the javelin (providing the average force is not significantly reduced).

A tennis player serves a ball at a speed of 224km/h. The ball reached the other player 20m across the court - how long did it take for the ball to reach the other player.

In sport and human movement it is always beneficial to create large amounts of impulse.

A basketball player exerts a downward force of 2550 N during a cutting movement in which the coefficient of static friction (µs) between their shoe and the court surface is 0.95. What is the maximal sideways force that the player can exert before their shoe slides on the surface?

When a person is running they apply a force to the ground through their foot strike that occurs in the transverse, frontal and sagittal planes. What is the name of the resultant force that allows us to propel ourselves forward (or in the direction of the run)?

Rearrange the following equation (found in the section 'uniformly accelerated and projectile motion') to calculate how long it would take for an object to reach the ground when dropped from a height of 3.5m. D = V₁t + ½at² where: D = Distance from ground (3.5m) V₁ = Initial velocity (0) t = time in flight a = acceleration (9.81m/s²)

The formula derived from Newton's second law of motion is F = ma.

Which of the following equations represents impulse (as equal to the change in momentum)

When a force is applied to an object, such as the force applied to a golf ball from a golf club, it is being accelerated (i.e. from the unmoving to moving). Once the ball leaves the club and the force is no longer applied, the ball is no longer accelerating and moves at a constant horizontal velocity (in the absence of air resistance).

A bobsleigh has a mass of 150 kg. The mass of its two crew members are 95 kg and 98 kg. What is the momentum of the bobsleigh and crew if it is travelling at 8 m/s.

A rugby player runs into a head-on tackle with another player that is running with the ball during a game. Player A (going for tackle) has a body mass of 98kg and runs at a velocity of 3.5 m/s. Player B (carrying the ball) has a body mass of 82kg and runs at a velocity of 4 m/s. Use the formula 'momentum = mass x velocity' (p = m × v) to calculate the linear momentum of each player as they run and comment on the implications of the results on the possible outcomes of the tackle.

Name three things that may affect the forces that are applied to the ground through foot strike during running (and therefore influencing the ground reaction force).

When performing a vertical jump on a force plate there are several interesting features of the force trace. At the beginning of the jump the force trace will become negative (i.e. it drops below the 1 × body weight line). Briefly describe what is happening during this part of the movement and why it is seen as a negative value on the force trace.

Most of the time in human movement, the effect of air resistance is considered negligible. Name two sporting examples where the effect of air resistance may be significant.