# Physics - Forces

AQA GSCE Old specification physics P2

- Created by: EMayH
- Created on: 03-04-10 12:07

## Question 1.

What can you say about the forces acting on a stationary object or an object travelling at a constant speed?

## Answer 1.

They are equal and opposite

## Question 2.

What is the unit of force?

## Answer 2.

The Newton (N)

## Question 3.

What is the 'resultant force'?

## Answer 3.

A number of forces acting on an object that are replaced by a single force that has the same effect as the original forces acting together.

## Question 4.

What happens if the resultant force is zero?

## Answer 4.

The object remains stationary if it was at rest

Or

Continues to move at the same speed in the same direction if it was already moving.

## Question 5.

What is the equation for resultant force?

## Answer 5.

Resultant force = mass x acceleration

(newtons,N) (kg) (m/s squared)

## Question 6.

What happens if the resultant force is in the same direction as the velocity?

## Answer 6.

The velocity of the object increases. This is positive acceleration.

## Question 7.

What happens if the resultant force is opposite to the direction of the velocity?

## Answer 7.

The velocity of the object decreases and we call this negative acceleration (or decceleration)

## Question 8.

Name three factors that increase thinking distance.

## Answer 8.

- Tiredness,
- Alcohol
- Drugs

All of these increase reaction times

## Question 9.

Name three factors that increase braking distance.

## Answer 9.

- The speed the vehicle is travelling - faster = bigger braking distance
- The road/ weather conditions - icy or wet roads mean the driver has to break with less force to avoid skidding therefore increasing braking distance
- Contition of the vehicle - eg. worn tyre treads reduce friction - increase braking distance.

## Question 10.

What is the equation for stopping distance?

## Answer 10.

Stopping distance = thinking distance + braking distance

## Question 11.

What is the difference between mass and weight?

## Answer 11.

Weight = The force of gravity on an object and is measured in Newtons (N)

Mass = The quantity of matter in an object and is measured in grams/kilograms (g/kg)

## Question 12.

What is gravitational field strength and what is it measured in?

## Answer 12.

Gravitational field strength is the force of gravity on a 1kg object at the place the object is. The unit of gravitational field strength is the newton per kilogram (N/kg)

## Question 13.

What is the equation for weight?

## Answer 13.

Weight = mass x gravitational field strength

(newtons,N) (kilograms,kg) x(newtons/kilogram,N/kg)

## Question 14.

Explain terminal velocity, saying what it is and refering to graph shapes.

## Answer 14.

Terminal Velocity is when an object reaches a constant velocity as the drag force is equal and opposite to its weight. At terminal velocity, both the resultant force and acceleration are zero. On a graph you can tell when an object has reached terminal velocity because it flattens out.

## Question 15.

What value (approximately) is the Earth's gravitational field strength at its surface?

## Answer 15.

About 10N

## Question 16.

If an object falls freely, what (approximately) is its acceleration?

## Answer 16.

Acceleration = resultant force/mass

= 10N (force of gravity) / 1kg

= 10m/s squared

## Question 17.

Does the acceleration of an object increase or decrease as it falls through a fluid, and why?

## Answer 17.

Decreases, because the drag force increases and consequently the resultant force on it decreases.

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