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Andrew skis down a hill - Edexcel - GCSE Physics - Question 2 - 2013 - Paper 1
Question 2
Andrew skis down a hill. (a) Andrew starts from the top of the hill and his speed increases as he goes downhill. He controls his speed and direction by using his s... show full transcript
Worked Solution & Example Answer:Andrew skis down a hill - Edexcel - GCSE Physics - Question 2 - 2013 - Paper 1
Step 1
Describe the energy changes that happen between starting and stopping.
Answer
When Andrew starts skiing down the hill, he begins with gravitational potential energy due to his height at the top of the hill. As he descends, this gravitational potential energy is converted into kinetic energy, increasing his speed. Some energy is also transformed into heat and sound due to air resistance and friction as he moves downhill. When Andrew brings himself to a stop at the bottom, the kinetic energy is dissipated, mainly as heat energy, transferred to his surroundings.
Step 2
His mass is 67 kg. Show that his momentum is about 2000 kg m/s when his velocity is 31 m/s.
Answer
To find momentum, we use the formula:
where:
- is momentum,
- is mass, and
- is velocity.
Given:
- Mass () = 67 kg
- Velocity () = 31 m/s
Substituting these values in:
Thus, Andrew's momentum is approximately 2000 kg m/s.
Step 3
Calculate the average force on Andrew as he slows down.
Answer
To calculate the average force acting on Andrew, we apply the formula relating force and momentum:
F = rac{ ext{change in momentum}}{ ext{time}}
From part (ii), Andrew's initial momentum is 2000 kg m/s and it reduces to 0 kg m/s. Therefore, the change in momentum is:
The time taken to slow down is given as 2.3 s. Thus, the average force can be calculated as:
F = rac{2000}{2.3} ext{ N} \approx 870 ext{ N}
Step 4
Use ideas about force and momentum to explain why he is not injured.
Answer
Andrew is not injured because the force acting on him during the fall is relatively small due to the large time over which the fall occurs. Although he is moving quickly initially, the impact time when he falls is long, allowing the force to be distributed over a longer duration. This gradual deceleration reduces the severity of the force experienced, hence preventing injury.