To calculate the braking speed of a car, we can use the physical formula to solve this problem. Here, we will apply Newton's second law and the conservation law of kinetic energy. First, we need to find out the friction force, and then use Newton's second law to calculate the deceleration. Finally, we use the law of conservation of kinetic energy to calculate the speed of the car when braking.

Calculate friction (F _ friction)

Friction = friction coefficient × normal force

Since the car is driving horizontally on the ground, the normal force is equal to gravity:

Normal force = mass × acceleration of gravity

Mass = 2 tons = 2000kg (1 ton =1000kg)

Gravity acceleration g = 9.8 1 m/s?

Normal force = 2000 kg × 9.8 1 m/s? = 19620 Newton

Friction = 0.7×19620n =13734n.

Calculate deceleration (a)

Newton's second law: F = ma

a = F/m = 13734N/2000kg = 6.867m/s？

Calculate the speed (v) of the car when braking.

Braking distance (seconds) = 49.7m.

We can use the following formula (law of conservation of kinetic energy) to calculate the initial velocity:

v？ = u？ + 2as

Where, V is the speed after braking, U is the speed before braking, A is the deceleration, and S is the braking distance. Since the car stops after braking, v = 0.

0 = u？ +2× (-6.867m/s? ) × 49.7m.

u？ = 2× 6.867m/s? × 49.7m.

u？ ≈ 682.52

U ? 682.52 ? 26.12m/s

Therefore, the braking speed of the car is about 26.12 m/s.