uctedulcourses/1267291/quizzes/1651738/take Secure I 0.1 pts D Question 10 A car

Question

uctedulcourses/1267291/quizzes/1651738/take Secure I 0.1 pts D Question 10 A car and a lorry are moving with the same kinetic energy. They are brought to rest by applying brakes, which provide equal retarding forces. The distance covered by them before coming to rest will be O equal O directly proportional to their masses O inversely proportional to their masses O inversely proportional to the square of their masses D Question 11 0.1 pts A 30 gm bullet traveling with 500 m/s penetrates 12 cm into a wooden block. The average force exerted 26.000 N O 31,000N 36,000 N 21,000 MacBook Air 5 6 7 9

Explanation / Answer

Question 10

Let ML and vL be the mass and velocity of the lorry respectively.

Let MC and vC be the mass and velocity of the car respectively.

Since they are moving with the same kinetic energy,

0.5ML vL2 = 0.5MC vC2 = KE (Say)

Now, since ML > MC, we have vL < vC

Let SL be the distance travelled by the lorry before coming to rest. Then,

0 = vL2 - 2aLSL, where aL is the deceleration of the lorry.

Then, SL = vL2 / 2aL = (2KE)/(2ML aL) = KE/(ML aL) -------(1)

Let aC be the deceleration of the car and FR be the retarding force. Then,

MLaL = MCaC = FR

From Eq (1), we have, SL = KE / FR = constant = SC, where SC is the distance travelled by the car.

So, the distance covered by them before coming to rest will be equal.

Question 11

Mass, m = 30 gm = 0.030 kg

velocity, v = 500 m/s

distance, s = 12 cm = 0.12 m

Let the deceleration be `a'. Then,

0 = v2 - 2as => a = v2/2s = (5002)/(2 x 0.12) m/s2

So, force exerted is , F = ma = (0.030 x 5002)/(2 x 0.12) N = 31250 N ~ 31,000 N

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