MYTUTOR SUBJECT ANSWERS

811 views

A model truck A of mass 1.2 kg is travelling due west with a speed of 0.90 m/s . A second truck B of mass 4.0 kg is travelling due east towards A with a speed of 0.35 m/s .

a)  Calculate the magnitude of the total momentum of the trucks. 

The momentum (p) is the mass (m) of an object multiplied by its velocity (v). 

p = m x v

Velocity is different to speed, because it has a direction. Fortunately, the trucks in the question are travelling in exactly opposite directions, so we can express their velocities, one compared to the other, as one being negative, and the other one being positive. Lets decide to make "travelling due east" positive, and "travelling due west" negative. 

momentum of truck A = mass of truck A x velocity of truck A
p1 = m1 x v1 = 1.2 kg x - 0.90 m/s = - 1.08 kg.m/s

momentum of truck B = mass of truck B x velocity of truck B
p2 = m2 x v2 = 4.0 kg x 0.35 m/s = 1.4 kg.m/s

total momentum of the trucks = momentum of truck A + momentum of truck B
p(total) = p1 + p2 = - 1.08 kg.m/s + 1.4 kg.m/s = 0.32 kg.m/s 

The total momentum is positive, which means that it is in the east direction, or in the direction of truck B.

If we look back at the numbers, we see that the mass of truck B is 3.3 times bigger than mass of truck A (4.0 / 1.2 = 3.3), while the speed of truck B is only 2.6 times smaller than the speed of truck A (9.0 / 0.35 = 2.6), so it makes sense that truck B has greater momentum.

b) The trucks collide and stick together. Determine their velocity after the collision. 

The trucks stick together after collision. When this happens we can assume that they become one big truck. The mass of the new truck will be:

mass of big truck = mass of truck A + mass of truck B
m3 = m1 + m2 = 1.2 kg + 4.0 kg = 5.2 kg

We also assume that the trucks are in a closed system, meaning that the total momentum before the collision is the same as the total momentum after the collision. We can write this as:

p1 + p2 = p3 

or 

m1v1 + m2v2 = m3v3

The question asks us to determine the velocity after the collision. We can therefore rearrange the equation above to solve for v3.

v3 = (m1v1 + m2v2) / m3 = 0.32 kg.m/s / 5.2 kg = 0.06 m/s

After the collision, the two trucks will be travelling together due east at a speed of 0.06 m/s.

Anna L. GCSE French tutor, A Level French tutor, GCSE Maths tutor, A ...

1 year ago

Answered by Anna, an A Level Physics tutor with MyTutor


Still stuck? Get one-to-one help from a personally interviewed subject specialist

89 SUBJECT SPECIALISTS

£20 /hr

Jake A.

Degree: Engineering (Masters) - Warwick University

Subjects offered:Physics, Maths+ 2 more

Physics
Maths
Further Mathematics
Chemistry

“Who am I? Hey! I’m a personal tutor, general maths enthusiast and am presently studying Engineering at Warwick University. I currently tutor students for Maths / Physics A-level along with Maths, Physics and Chemistry GCSE. I have a g...”

£22 /hr

Jonathan D.

Degree: Natural Sciences (Physical) (Bachelors) - Cambridge University

Subjects offered:Physics, Maths+ 1 more

Physics
Maths
Chemistry

“2nd year Natural Sciences student at Cambridge - massively passionate about all things Maths and Science, and I would love to be able to help!”

£30 /hr

Duncan L.

Degree: MPhys Physics with Study in Australia (Masters) - Exeter University

Subjects offered:Physics, Maths+ 1 more

Physics
Maths
-Personal Statements-

“I am a first year physicist at the University of Exeter, I love my course and I am keen to share my knowledge and experience to help you with GCSE maths and physics.”

About the author

Anna L.

Currently unavailable: for regular students

Degree: Water Informatics Science and Engineering Centre for Doctoral Training (Doctorate) - Exeter University

Subjects offered:Physics, Maths+ 1 more

Physics
Maths
French

“I am a postgraduate student at the University of Bristol. I have a constant curiosity to understand how things work, which is why in school I most enjoyed physics. I then did an undergraduate degree in civil engineering, before focusi...”

You may also like...

Posts by Anna

A model truck A of mass 1.2 kg is travelling due west with a speed of 0.90 m/s . A second truck B of mass 4.0 kg is travelling due east towards A with a speed of 0.35 m/s .

A particle that moves uniformly in a circular path is accelerating yet moving at a constant speed. Explain this statement.

Other A Level Physics questions

Calculating the hydrostatic force on a submerged body

Why does current split between branches of a parallel circuit, but voltage remains the same for each branch?

Explain the workings of a mass spectrometer

A sample of pure gold has a density of 19300 kgm^-3. If the density of a gold nucleus is 1.47x10^17Kgm^-3, discuss what this implies about the structure of the gold atom. [4 marks]

View A Level Physics tutors

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok