Dynamics QuizDynamics Quiz

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Question 1Question 1

The balloon of weight 500 N (mass 50 kg)The balloon of weight 500 N (mass 50 kg)

moves downwards with a constant velocity of moves downwards with a constant velocity of

2m/s . Assume the only other force acting on the2m/s . Assume the only other force acting on the

object is the air resistance.object is the air resistance.

What is the resultant force acting on the balloon?What is the resultant force acting on the balloon?

A. 0 NA. 0 N B. 100 NB. 100 N

C. 400 NC. 400 N D. 500 ND. 500 N

Option AOption A

You are right!!!You are right!!!

Since it is moving with constant velocity, the Since it is moving with constant velocity, the acceleration will be 0. Thus the resultant acceleration will be 0. Thus the resultant force is 0 N.force is 0 N.

Go to the Go to the question 2question 2

Option BOption B

The acceleration is not 2m/sThe acceleration is not 2m/s2.2.

The balloon is moving with constant velocity of 2 The balloon is moving with constant velocity of 2 m/s. m/s.

Hint : What is the acceleration of an object with Hint : What is the acceleration of an object with constant velocity?constant velocity?

Go back to Go back to Question 1Question 1

Option COption C

The acceleration is not 2m/sThe acceleration is not 2m/s2.2.

The balloon is moving with constant velocity of 2 The balloon is moving with constant velocity of 2 m/s. m/s.

Hint : What is the acceleration of an object with Hint : What is the acceleration of an object with constant velocity?constant velocity?

Go back to Go back to Question 1Question 1

Option DOption D

The question asks for the The question asks for the resultant force not resultant force not the opposing air resistance.the opposing air resistance.

Read the question carefully.Read the question carefully.

Go back to Go back to Question 1Question 1

Question 2Question 2

The balloon of weight 500 N (mass 50 kg)The balloon of weight 500 N (mass 50 kg)

moves downwards with a constant velocity of moves downwards with a constant velocity of

2m/s . Assume the only other force acting on the2m/s . Assume the only other force acting on the

object is the air resistance.object is the air resistance.

What is the magnitude of the air resistance ?What is the magnitude of the air resistance ?

A. 0 NA. 0 N B. 100 NB. 100 N

C. 50 NC. 50 N D. 500 ND. 500 N

Option AOption A

The question asks for the The question asks for the opposing air opposing air resistance and not the resultant force.resistance and not the resultant force.

Read the question carefully.Read the question carefully.

Go back to the Go back to the Question 2Question 2

Option BOption B

The acceleration is not 2m/sThe acceleration is not 2m/s2.2.

The balloon is moving with constant velocity of 2 The balloon is moving with constant velocity of 2 m/s. m/s.

Hint : What is the acceleration of an object with Hint : What is the acceleration of an object with constant velocity?constant velocity?

Go back to Go back to Question 2Question 2

Option COption C

Mass is not a force. Mass is not a force.

Weight is a force!!!!Weight is a force!!!!

Go back to Go back to Question 2Question 2

Option DOption D

You are right!!!You are right!!!

The balloon is moving with constant velocityThe balloon is moving with constant velocityand the resultant force is 0 N.and the resultant force is 0 N.

Consider upwards as positiveConsider upwards as positive

Air resistance – W = 0 Air resistance – W = 0 Air resistance – 500 = 0Air resistance – 500 = 0Air resistance = 500 NAir resistance = 500 N(Take note that Weight is a force but not mass).(Take note that Weight is a force but not mass).

Go to Go to question 3question 3W = 500 N

Air resistance

Question 3Question 3A car of mass 800 kg is being driven along a level road. The engine supplies a driving force of 3600 N and the resistive force is 2000 N. What is the acceleration of the car?

2000 N3600 N

A.2.0 m/s2 B. 2.5 m/s2

B. 4.5 m/s2 C. 7.0 m/s2

Option AOption A

You are right!!!You are right!!!Consider left as positive.Consider left as positive.Let the acceleration be a.Let the acceleration be a.

Resultant force Resultant force = 3600 N + (-2000 N) = 1600 N= 3600 N + (-2000 N) = 1600 N

Resultant force = mass x acceleration = 800 aResultant force = mass x acceleration = 800 a

800 a = 1600 800 a = 1600 a = 2 m/sa = 2 m/s22

Go to Go to Question 4Question 4

2000 N3600 N

Left as positive

Option BOption B

There are two forces (resistive and a forward force) acting onThere are two forces (resistive and a forward force) acting onthe object.the object.

The resultant force is not 2000 N (resistive force) The resultant force is not 2000 N (resistive force)

Remember : Resultant force = mass x accelerationRemember : Resultant force = mass x acceleration

Hint : Find the resultant forceHint : Find the resultant force

Go back to Go back to Question 3Question 3

2000 N3600 N

Option COption C

There are two forces (resistive and a forward force) acting on the object.There are two forces (resistive and a forward force) acting on the object.

The resultant force is not 3600 N (forward force)The resultant force is not 3600 N (forward force)

Remember : Resultant force = mass x accelerationRemember : Resultant force = mass x acceleration

Hint : Find the resultant forceHint : Find the resultant force

Go back to Go back to Question 3Question 3

2000 N3600 N

Option DOption D

There are two forces (resistive and a forward force) acting onThere are two forces (resistive and a forward force) acting onthe object.the object.

The resultant force is not 5600 N as the two forces are actingThe resultant force is not 5600 N as the two forces are actingin the opposite directionin the opposite direction

Remember : Resultant force = mass x accelerationRemember : Resultant force = mass x acceleration

Hint : Find the resultant forceHint : Find the resultant force

Go back to Go back to Question 3Question 3

2000 N3600 N

Question 4Question 4The car has mass 800 kg . The combined The car has mass 800 kg . The combined

forces of friction and air resistance is 400 N forces of friction and air resistance is 400 N and the acceleration (to the left) is 0.4 m/sand the acceleration (to the left) is 0.4 m/s22. . What is the forward driving force ?What is the forward driving force ?

Forward driving force

friction

Air resistance

A. 320 N B. 400 NB. 480 N C. 720 N

Option AOption A

The questions asks for forward force not the The questions asks for forward force not the resultant force!!!resultant force!!!

The is more than 1 force acting on the car and theThe is more than 1 force acting on the car and theresultant force is not equal to the forward force!!!resultant force is not equal to the forward force!!!

Read the question carefully.Read the question carefully.

Go back to Go back to Question 4Question 4

Air resistanceForward force

Left as positive

friction

Option BOption B

The resultant force is not 0 !!! The car isThe resultant force is not 0 !!! The car isaccelerating (to the left) at a rate of 0.4 m/saccelerating (to the left) at a rate of 0.4 m/s22

Go back to Question 4Go back to Question 4

Air resistanceForward force

Left as positive

friction

Option COption C

The acceleration is to the left !!!The acceleration is to the left !!!

Read the question carefully.Read the question carefully.

Go back to Question 4Go back to Question 4

Air resistanceForward force

Left as positive

friction

Option DOption D

You are right!!!You are right!!!Consider left as positive.Consider left as positive.

Resultant force Resultant force = Forward Force + (-400N) = Forward Force - 400= Forward Force + (-400N) = Forward Force - 400

Resultant force = mass x acceleration = 800(0.4) = 320 NResultant force = mass x acceleration = 800(0.4) = 320 NForward Force - 400 = 320 NForward Force - 400 = 320 N

Forward Force = 720 NForward Force = 720 N

Left as positive

Air resistanceForward force

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Now for the more challenging questions!!!Now for the more challenging questions!!!

Please proceed to do the Chpt 3 Dynamics Please proceed to do the Chpt 3 Dynamics Worksheet Pg 3 (Question 3 – 8)Worksheet Pg 3 (Question 3 – 8)

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