# Try these

1. What is centripetal acceleration?
2. How does the law of displacement work in design?
3. Two identical cars collide head on. Each car is traveling at 100 km/h. The impact force on each car is the same as hitting a solid wall at:

(a) 100 km/h
(b) 200 km/h
(c) 150 km/h
(d) 50 km/h

[H/T real-world physics]

## 13 comments for “Try these”

1. Mark in Mayenne
March 18, 2019 at 18:53

The acceleration towards the centre of circular motion

What makes boats float?

A 100 mph

• March 18, 2019 at 20:12

There’s a man who knows his stuff.

• Doonhamer
March 19, 2019 at 06:31

But not his units.

2. Chuckles
March 18, 2019 at 20:32

1. The acceleration fro spinning a flower
2. When a body is totally or partially immersed in water, the telephone rings
3. a different location, where there is no other vehicle involved

3. March 18, 2019 at 21:50

Useful data in that context – one cubic foot of water is around 63lbs, about the same as a 4×8 sheet of half inch ply.

For every 15 sq ft of sail, you need another block [purchase], unless using a winch. 150 sq ft therefore needs 10:1.

4. dearieme
March 18, 2019 at 21:52

Are we being asked to pretend that a car is as rigid as a “solid wall”?

I loathe these sort of half-arsed questions where the problem is always under-specified.

• March 18, 2019 at 21:54

Quite rightly too – one should be in high dudgeon over such things, a bit like Tessa with the poisonous one this evening.

• Chuckles
March 19, 2019 at 07:51

Assume a spherical car…

• dearieme
March 19, 2019 at 10:29

and perfectly elastic.

5. ivan
March 18, 2019 at 22:05

#3 is rather ambiguous because neither car is a solid wall – you have the crumple factor applied twice and it would also depend on the solidity of the wall, a brick wall one brick thick thick might not even stop the car whereas a concrete wall one meter thick would and also push the engine back into the passenger space.

6. March 18, 2019 at 22:09

Y-e-e-e-s-s-s but you’d still not be well after the car crash.

• Andy5759
March 19, 2019 at 00:39

Do we permit blind people to drive cars? Or, are there still invisible walls around, I haven’t seen any since writing off a few motorcycles. Didn’t see them then either. My brain is well ‘urting, again.

Do boat builders have to experience a Eureka moment?

• March 19, 2019 at 13:38

I’ll tell you in the next few days.

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