Question

A 2000kg car travelling at 72km/h runs into a concrete wall and stops in 0.05s. What is the magnitude force that the wall will exert on the car? What would be the force exerted on the wall by the car

Answer 1

Given:

A 2000kg car travelling at 72km/h runs into a concrete wall and stops in 0.05s.

To find:

Force exerted by wall on car and vice-versa?

Calculation:

Let acceleration be 'a':

• 72 km/hr = 72 × 5/18 = 20 m/s.

$a = \dfrac{0 - 20}{0.05}$

$\implies a = - \dfrac{ 20}{0.05}$

$\implies a = - 400 \: m {s}^{ - 2}$

Now, force exerted by wall on car:

$F = m \times a$

$\implies F = 2000 \times ( - 400)$

$\implies F = - 800 \: kN$

So, force exerted by wall on car is -800 kN.

• According to Newton's 2nd Law, force exerted by car on wall is 800 kN.

Answer 2

Explanation:

Given:

A 2000kg car travelling at 72km/h runs into a concrete wall and stops in 0.05s.

To find:

Force exerted by wall on car and vice-versa?

Calculation:

Let acceleration be 'a':

72 km/hr = 72 × 5/18 = 20 m/s.

a = \dfrac{0 - 20}{0.05}a=

0.05

0−20

\implies a = - \dfrac{ 20}{0.05}⟹a=−

0.05

20

\implies a = - 400 \: m {s}^{ - 2}⟹a=−400ms

−2

Now, force exerted by wall on car:

F = m \times aF=m×a

\implies F = 2000 \times ( - 400)⟹F=2000×(−400)

\implies F = - 800 \: kN⟹F=−800kN

So, force exerted by wall on car is -800 kN.

According to Newton's 2nd Law, force exerted by car on wall is 800 kN.