1.5.1 Effects of forces (3)
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1.
A block of wood is resting on a horizontal surface. A force of 10N is applied to the block, but it does not move. Describe the forces acting on the block and explain why the block remains stationary. Also, explain how the frictional force would change if the block was replaced with a block of felt.
When the block of wood is resting on the horizontal surface and no force is applied, several forces act on it:
- Weight (W): This is the force due to gravity acting downwards on the block. It's equal to mass (m) times the acceleration due to gravity (g), i.e., W = mg.
- Normal Force (N): This is the force exerted by the surface on the block, acting upwards. In this case, the normal force is equal to the weight of the block (N = W).
- Frictional Force (Ff): This force acts horizontally, opposing the potential motion of the block. Since the block is stationary, the frictional force is equal in magnitude and opposite in direction to the applied force.
The block remains stationary because the applied force (10N) is equal in magnitude to the frictional force acting on it. The frictional force is preventing the block from moving.
If the block of wood was replaced with a block of felt, the frictional force would increase. Felt has a much higher coefficient of friction than wood. This means that for the same normal force (the weight of the block), the frictional force would be greater, and therefore the block would be more difficult to move. The frictional force would be larger, potentially requiring a greater applied force to overcome it.
2.
A student pushes a shopping trolley with a mass of 15 kg across a smooth floor. The trolley accelerates at a rate of 0.8 m/s2. Calculate the force the student exerts on the trolley.
Given:
- Mass (m) = 15 kg
- Acceleration (a) = 0.8 m/s2
- Force (F) = ?
Equation: F = m a
Calculation: F = 15 kg × 0.8 m/s2 = 12 N
Answer: The student exerts a force of 12 N on the trolley.
3.
A student plotted the load-extension graph for a metal bar. The graph shows a straight-line section passing through the origin.
a) What does the presence of a straight-line section passing through the origin on a load-extension graph indicate about the material?
b) Identify this point on the load-extension graph.
a) The presence of a straight-line section passing through the origin on a load-extension graph indicates that the material is behaving elastically. This means that the extension of the material is directly proportional to the applied load, and the material will return to its original shape when the load is removed.
b) This point on the load-extension graph is called the limit of proportionality. It is the point where the slope of the load-extension curve is constant and the material behaves linearly.