Demonstrate understanding aspects of mechanics Credits: 4

Target Language or Knowledge:

Question 1 The Ice hockey game An ice hockey player uses an ice hockey stick to push or hit a puck. The puck has a mass of 0.17kg. a. Calculate the force required to give the puck an acceleration of 710 ms-2.
120N
The graphs opposite show the motion of a player during 12 seconds of an ice hockey game. Both graphs show the same motion. b. Using both graphs, fully describe the motion of section A, B, C, D. No calculations required. You should use speed, time and distance values from the graph.
Section A: Player is _accelerating_ from 0-0.16 m/s in 0.8 s. She reaches a _distance_ of approx. 0.6 m Section B: Player is travelling at a _steady_ speed of 0.16 m/s for 3.0 s. She reaches a _distance_ of approx. 5.5 m Section C: Player is _decelerating_ from 0.16 - 0 m/s in 0.4 s. She reaches a _distance_ of approx. 5.8 m Section D: Player is _stationary_ for 1.6 s at a _distance_ of approx. 5.7 m
c. Using either graph describe the similarities and differences in the motion of the player at Section D and Section H. Use values from the graphs
Both _stationary_ _v=0._ _ Different_ _distance_ D is at approx. _5.7m,_ H is at _10m._ Both are _changing_ _speed,_ therefore both are _accelerating,_ but C is _negative_ and E is _positive_
d. Using either graph and by making calculations, describe the similarities and differences in the motion of the player at Section C and Section E. Use values from the graphs –calculations are required.
C _decelerating_quickly_ from 1.6 ms-1 to 0 in 0.4 s a=v/t = 0-1.6/0.4 = -4 ms-2 E accelerating _more_slowly_ from 0 to 1.2 ms-1 in 1.2 s a=v/t = 1.2-0/1.2 = 1 ms-2 Steep slope _large_acceleration,_ shallow slope small __acceleration_
Using the speed-time graph, calculate the distance travelled in the first 4.2s.
5.58m
Question 2 Curling Curling is a game played on ice with large, heavy curling stones. Two players are talking about their curling stones. One asks the other how much his stone weighs. He replies “my stone weighs 18.2 kilograms” a. Explain what is wrong with this answer. In your answer you should • explain the difference between mass and weight
Mass is the _amount_ of _matter_ an object has. It is measured in _kilograms._ Weight is the _amount_ of _gravitational_ _force_ that is applied to the object. It is measure in _Newtons_ The player has given the _mass_ (=18.2 kg) not the _weight._ Weight is the effect of the _gravitational_ _force_ on a _mass._
Two players are talking about their curling stones. One asks the other how much his stone weighs. He replies “my stone weighs 18.2 kilograms” • calculate the correct answer to the players’ question.
182N
The player has a choice of two different stones. Either one that is 18.2 kg or one that is heavier. The player is required to accelerate the stone from rest to 4 ms-1. He does this in a distance of 3.6m. b. Explain the effect that choosing the heavier stone will have on the power required to accelerate it. You should justify your answer using equations, however calculations are required
A heavier stone has more _mass._ Since _a=F/m,_ an object with more _mass_ will require more _force_ for the same _acceleration._ If the _distance_ is the same, but the _force_ is greater, since W=Fd the amount of _work_ done on the stone is _greater._ Since _P=E/t_ and W=E, if _energy_ increases, the power must _increase_ also. Or A heavier stone has more _mass._ The player transfers _energy_ to the _stone,_ giving the stone _kinetic_ _energy._ Since _E=1/2mv2,_ the stone with the greater mass will have more _kinetic_ _energy._ Since P=E/t if energy increases, the _power_ must increase also
The stone in diagram c is travelling at an initial speed of 4 ms-1. It takes 22 seconds to stop. Calculate the unbalanced force on the stone.
-3.31N
Question 3 Luge Riding. Naseby luge track in central Otago is a snow track that can be ridden by a one person sled. Jack (mass 62 kg) is going luging. The luge sled weighs 80N. Before going down the track, he is standing on soft snow and the luge sled is resting the same soft snow. Jack notices that the sled makes shallow indents into the snow and his boots are sinking into the snow a couple of centimetres. He calculates the pressure he exerts on the snow is approximately 6900 N m-2. He is worried that if he adds his weight by sitting on the sled, it will sink further into the snow as it has very narrow runners. a. Jack sits on the sled on the snow. Determine if the sled will sink into the snow more than, less than or the same amount his boots do. • Begin by calculating the pressure exerted by Jack and the sled on the snow.
5400 Nm-2
Jack (mass 62 kg) is going luging. The luge sled weighs 80N. Before going down the track, he is standing on soft snow and the luge sled is resting the same soft snow. Jack notices that the sled makes shallow indents into the snow and his boots are sinking into the snow a couple of centimetres. He calculates the pressure he exerts on the snow is approximately 6900 N m-2. He is worried that if he adds his weight by sitting on the sled, it will sink further into the snow as it has very narrow runners . Jack sits on the sled on the snow. Determine if the sled will sink into the snow more than, less than or the same amount his boots do using the previous answer to help.
This pressure is _less_ than 6900 with just his boots, so the sled will _sink_ into the snow, but _not_ as much as the boots. This is because, although the _weight_ is _greater_ _(620+80=700N,_ the sled runner's total _surface_ _area_ touching the snow is _greater_ than the boots, giving a slightly _lower_ pressure.
The track is 360m long and the start is 22.5 m higher than the finish. Jack has to carry the luge sled up some steps to get to the start of the track. b. Calculate the work done on the sled to carry it up the steps. State the unit.
1800J
He then pushes the sled at a constant speed along a flat section 30 m long. c. Explain what work is done (if any) on this section. No calculations are required, but you should refer to a relevant formula
No _work_ done as no _energy_ _transferred_ in the direction of the _force_ (no _increase_ of Ek or Ep)
Jack is ready to go. He sets off at the beginning of the slope and his speed increases as he goes down the slope. By the end of the slope he is travelling at 54 km/h (15 m/s). d. Calculate the theoretical maximum speed he could reach
21.2〖ms〗^(-1)
Jack is ready to go. He sets off at the beginning of the slope and his speed increases as he goes down the slope. By the end of the slope he is travelling at 54 km/h (15 m/s). d. use the previous answer and compare it with 54 km/h. Explain why these values are different.
This is _greater_ not _less_ than the actual 15m/s. This is because some of the _potential_ _energy_ will be transferred to _heat_ in the runners and snow (and air molecules) as _friction_ and _wind_ _resistance_