Photo AI
6 (a) Figure 11 shows a person doing a push-up exercise - Edexcel - GCSE Physics - Question 6 - 2023 - Paper 2
Question 6
6 (a) Figure 11 shows a person doing a push-up exercise. An upward force is used to cause rotation about a pivot. Which row of the table is correct for this rotati... show full transcript
Worked Solution & Example Answer:6 (a) Figure 11 shows a person doing a push-up exercise - Edexcel - GCSE Physics - Question 6 - 2023 - Paper 2
Step 1
6 (b) (i) Use the principle of moments to show that the system shown in Figure 13 is in equilibrium.
Answer
To demonstrate that the system is in equilibrium, we need to apply the principle of moments. The principle states that for a system to be in equilibrium, the total moment (clockwise) about a pivot must equal the total moment (anticlockwise).
-
Calculate the clockwise moment created by the weight of the forearm:
-
Moment = Force × Distance
-
Weight of forearm = 23 N and distance from pivot (elbow joint) = 16 cm:
Moment = 23 N × 16 cm = 368 Ncm
-
-
The biceps muscle generates an upward force of 92 N at a distance of 4 cm from the elbow joint:
-
Moment = Force × Distance
Moment = 92 N × 4 cm = 368 Ncm
-
Combining both moments:
- Total clockwise moment = 368 Ncm (from biceps) + 368 Ncm (from forearm) = 736 Ncm
- Total anticlockwise moment = Weight of forearm acting at 16 cm = 368 Ncm.
Since the total clockwise and anticlockwise moments are equal, the system is in equilibrium.
Step 2
6 (b) (ii) Calculate the force from the muscle that is needed to keep the system in Figure 14 in equilibrium.
Answer
To find the force from the muscle required to keep the system in equilibrium when holding the ball, we again apply the principle of moments.
-
Calculate the total clockwise moment due to the weights:
-
Weight of the ball = 15 N acting at a distance of 32 cm from the elbow joint:
Moment due to the ball = 15 N × 32 cm = 480 Ncm
- Total moment due to the weight of the forearm is still 368 Ncm (as calculated before).
- Total clockwise moment = 480 Ncm + 368 Ncm = 848 Ncm
-
-
Now, using the force from the muscle which acts at a distance of 4 cm from the pivot to balance this:
-
Let F be the force from the muscle. The moment created by the muscle is:
Moment = F × 4 cm
Setting the total anticlockwise moment equal to the total clockwise moment:
F × 4 cm = 848 Ncm
F = rac{848 Ncm}{4 cm} = 212 N
-
Thus, the force from the muscle needed to maintain equilibrium is 212 N.
Step 3
6 (c) (i) Compare the upthrust on the ball in seawater with the upthrust on the same ball in fresh water.
Answer
The upthrust on the ball in seawater is greater than the upthrust on the ball in fresh water. This is because seawater is denser than fresh water, which results in a greater buoyant force acting on the ball when it is submerged.
Step 4
6 (c) (ii) Explain why there is less of the ball below the surface of the seawater than below the surface of the fresh water.
Answer
There is less of the ball below the surface of the seawater compared to the fresh water due to the density difference between the two liquids. The weight of the water displaced by the ball determines the upthrust. Since seawater is denser than fresh water, it requires less volume of seawater to displace the same weight of water. As a result, the ball is less submerged in seawater than in fresh water.