1D Motion Practice (Kinematics)

On Halloween MIT students have a custom to through pumpkins off an 80m building.

However wasteful, it presents an excellent opportunity for physics problems.

What is the equation of acceleration?

Assumptions:

Positive direction is down

Acceleration due to gravity will be rounded to 10m/s^2

• a(t) = -10t

• a(t) = 10t

• a(t) = 10

• a(t) = -10

What is the equation of velocity?

Acceleration = a(t) = 10m/s^2. Integrate to get velocity.

Assumption: initial velocity is zero.

• v(t) = -10t

• v(t) = 10t

• v(t) = 10t + C

• v(t) = -10t + C

What is the equation of displacement?

Velocity = v(t) = 10t m/s. Integrate to get displacement.

Assumption: initial displacement is zero, positive direction is down

• y(t) = -10t+80

• y(t) = 10t^2

• y(t) = 5t^2

• y(t) = 5t^2 + 80

How many seconds does it take for the pumpkin to reach the ground?

y (t) = 5t^2

The height of the building is 80m.

• 2 seconds
• 4 seconds
• 6 seconds
• 10 seconds

The branch is initially 36cm. If you saw the branch with cosntant acceleration of 2cm/s^2.

How long will it take you to start falling?

• 8 seconds

• 2 seconds

• 6 seconds

Answer explanation

a = 2 cm/s^2

v = 2t cm/s

d = 2t^2/2 = t^2 cm

d = 36cm therefore t = 6sec

Two lovely ladies started walking towards each other at 9am and walked for 16km at constant speed of 8km/h.

How long was their covnersation if they finally part at noon?

• 1 hour

• 2 hours

• 11 hours

Answer explanation

They will walk 16km in 2 hours at constant speed of 2km/h. If they started at 9am, they will meet in 2 hours, i.e. 11am. If they part at 12pm, that means their conversation will be one hour.

A car moving from point A to point B is going 80km/h. It drives for 3 hours and punctures a tire on a rusty nail.

A bike moving from point B to point A is going 16km/h and rides for 3 hours before it punctures a tire on the same exact nail.

What is the distance between point A and B?

• 240km

• 288km

• 48km

One little boy has a night mare that he is chased by a tiger, a lion and a physics teacher. In his dream he can only run at 1km/h. The tiger can run at 2km/h, the lion at 3km/h and the physics teacher at 6km/h. The boy had a head start of 10km at 6am.

Who will catch him if at 8am his alarm will sound?

• Lion

• Tiger

• Physics Teacher

Answer explanation

The tiger is catching up at 1km/h, the lion at 2km/h and the teacher at 5km/h. Since there are 10km distance they need to cover and 2 hours to do it in, only the teacher will be able to catch the boy, but just barely!