Force and Laws of Motion | Chapter Assessment | English | Grade 9

Suppose an object has mass M is moving with a uniform velocity of v m/s for t seconds. If the force acting on the body is tripled, what happens to the acceleration of the body?

• The acceleration becomes 1/3

• The acceleration becomes tripled

• Acceleration remains the same

• None of the above

Answer explanation

Here the body is moving with uniform velocity, which means acceleration is zero. Hence, F = 0 Option 4 is correct

Tags

NGSS.HS-PS2-1

When you squeeze glue from a tube, which force is applied?

• Unbalanced Force

• Balanced Force

• Frictional Force

• Normal force

Answer explanation

When you squeeze the tube of gum, there is only change in the shape of the tube, so unbalanced force is applied. Hence option 2 is correct

Tags

NGSS.HS-PS2-1

A coin is tossed by a passenger in a moving train and the coin falls behind the person. What does it say about the motion of the train?

• The train is retarding

• The train is accelerating.

• The train is at rest.

• The train is in uniform motion

Answer explanation

If the motion of the train would have been uniform, the coin would have fallen on the passenger. If the train would have been retarding the coin would have fallen ahead of the passenger. As the coin falls behind the passenger, the train is accelerating

Tags

NGSS.HS-PS2-1

The law of conservation of momentum is applicable on which of the following?

• Two different objects

• Individual objects

• A system of objects

• None of the bove

Answer explanation

The law of conservation applies to a system of objects.

Tags

NGSS.HS-PS2-2

Chintu pushed a 10 kg sack of rice by applying some force. If the sack experiences frictional force of 15 N and moves with an acceleration of 15 m/s², what is the amount of force applied by Chintu?

• -100 N

• 135 N

• 150 N

• 165 N

Answer explanation

We know, F= m × a, Here, m= 10 kg, a = 15 m/s², Frictional force = 15N Let force applied be F F - Frictional force = m × a F - 15 = 10 × 15 F = 165 N

Tags

NGSS.HS-PS2-1

An object A of mass m with velocity v₁ hits another object B of mass n which is at rest. Calculate the final velocity of B if both the objects slide together.

• m+ n/ v₁+v₂

• mv₁/+n

• mv₁/(m +n)

• None of the above

Answer explanation

Both the object slide together, so final velocity is same for both We know, p1= p2 Initial momentum = Final momentum Initial momentum = Initial momentum of A + Initial momentum of B = mv₁ +nv₂ (let v₂ be initial velocity of B) = mv₁ Final momentum = final momentum of A + final momentum of B = mv +nv(let v be the final velocity) = v (m +n) p₁= p₂ mv₁ = v (m +n) v = mv₁/(m +n)

Tags

NGSS.HS-PS2-2

An object of mass 5 kg falls from a height of 50 cm. Calculate the momentum of the object just before it hits the ground.

• 5.3 kg m/s

• 15.8 kg m/s

• -15 kg m/s

• 45.5 kg m/s

Answer explanation

m= 5 kg, S= 50 cm= 0.5 m, u=0, a = 10 m/s² v² - u²= 2aS v² = 2aS v² = 2 × 10× 0.5 = 10 v = 3.16 m/s Momentum = 5 × 3.16 = 15.8 kg m/s

Tags

NGSS.HS-PS2-2