Forces (Newton's Law, Spring and Turning Effect of Forces)

​FORCE

By Mr Math n Physics

​What are Forces?

​A force is a push or a pull that one object exerts on another.
Its SI unit is the newton (N).

Effects of Some Forces

​Common Example of Forces

​Newton 2^nd Law :
ΣF = ma

​How does a force cause an object to move in a circular path?

Multiple Choice

Which moving object has a resultant force acting on it?

• a diver rising vertically through water at constant speed

• an aircraft circling an airport at constant speed

• a train going up a straight incline at constant speed

• a parachutist descending vertically at terminal velocity

Multiple Choice

On which ball is a non-zero resultant force acting?

Multiple Choice

A car of mass 1200 kg is travelling along a horizontal road. What is the acceleration of the car?

• 0.83 m/s²

• 1.2 m/s²

• 2.5 m/s²

• 3.3 m/s²

Multiple Choice

A cart has a mass of 10 kg. A boy pushes on the cart horizontally with a force of 50 N. The cart accelerates at 0.50 m/s². What is the frictional force acting on the cart

• 5.0 N

• 20 N

• 30 N

• 45 N

Multiple Choice

An object moves in a circle at constant speed. Which statement about the force needed on the object is correct?

• A force away from the centre of the circle keeps the object moving in the circle.

• A force in the direction of motion of the object keeps it moving in the circle.

• A force towards the centre of the circle keeps the object moving in the circle.

• No force is needed to keep the object moving at constant speed in the circle.

Multiple Choice

A car is travelling around a circular track at a constant speed, as shown. In which direction is the resultant force on the car?

• A

• B

• C

• D

Multiple Choice

A satellite orbits the Earth at constant speed in a circular orbit. Which statement is correct?

• The resultant force on the satellite is zero.

• The resultant force on the satellite is towards the Earth.

• The resultant force on the satellite is away from the Earth.

• The resultant force on the satellite is in the direction of its motion.

​Spring Force

​Hook

​Hooke's Law states that the force (F) needed to extend or compress an elastic object (like a spring) is directly proportional to the distance (x) it is extended or compressed, up to its elastic limit

​What is spring constant and limit of proportionality?

​a measure of a spring's stiffness, indicating the amount of force needed to stretch or compress it by a unit of length

​The limit of proportionality is the maximum stress or force a material can withstand while maintaining a linear relationship between stress and strain (or force and extension),

Multiple Choice

Hooke's Law states that the force (F) needed to extend or compress an elastic object (like a spring) is directly proportional to the distance (x) it is extended or compressed, up to its elastic limit

• A

• B

• C

• D

Multiple Choice

Look at the picture!

• A

• B

• C

• D

Multiple Choice

Different weights are hung from a spring. The diagram shows the original length of the spring, and the lengths when different weights are added. The extension of the spring is directly proportional to the weight hung from it.

What is the weight of W?

• 30 N

• 35 N

• 40 N

• 45 N

Multiple Choice

The extension-load graph for a spring is shown. The unstretched length of the spring is 17.0 cm.

When an object is hung from the spring, the length of the spring is 19.2 cm.

What is the weight of the object?

• 1.4 N

• 1.6 N

• 2.6 N

• 3.0 N

Multiple Choice

Objects with different masses are hung on a spring. The diagram shows how much the spring stretches.

The extension of the spring is directly proportional to the mass hung on it.

What is the mass of object M?

• 110 g

• 150 g

• 200 g

• 300 g

​Turning Effect of Forces

​Turning Effect of Force is knowing as Moment (SI unit : Nm)

​Defined as

Moment = Force x perpendicular distance of the force from the pivot

It can be

Clockwise

Anticlockwise

​What is the moment of a force?

Multiple Choice

A spanner is used to tighten a nut on a bicycle wheel. A force F is needed. How can the force F be reduced?

• Use a longer handle.

• Use a shorter handle.

• Use a thinner handle.

• Use a thicker handle.

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Multiple Choice

Two forces on a steering wheel acting in opposite directions. Determine direction of the Resultant moment!

• anti-clockwise direction

• clockwise direction

Multiple Choice

A wheelbarrow has a weight W of 140 N. Which vertical force F is needed to support the wheelbarrow in the position shown?

• 60 N

• 80 N

• 140 N

• 245 N

Multiple Choice

A uniform rod rests on a pivot at its centre. The rod is not attached to the pivot. Forces are then applied to the rod in four different ways, as shown. The weight of the rod can be ignored. Which diagram shows the rod in equilibrium?

• A

• B

• C

• D

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