Question

1. the displacement- time graph for two particles A and B are straight lines inclined at angles of 30 degree and 60 degree with the time axis . the ratio of velocities of VA : VB is a. 1:2 b. 1:root 3 c. root 3 :1 d. 1:3 2. a car travels from A to B at a speed of 20km/hr and returns at a speed of 30km/hr.the average speed of the car for the whole journey is a. 25 km/hr b. 24 km/hr c. 50 km/hr d.5km/hr 3.a car travels the first half of a distance between two places at a speed of 30km/hr and the second half of the distance at 50 km/hr .the average speed of the car for the whole journey is a.42.5 km/hr b. 40.0 km/hr c. 37.5 km/hr d. 35.0 km/hr 4.a car moves for half of its time at 80 km/h and for rest half of time at 40 km/h.total distance covered is 60 km. what is the average speed of the car ? a.60km/h b.80km/h c. 120km/h d. 180 km/h lz answer fast ..its urgent ..plz provide full method of doing

Answer 1

1st answer is d)3:1 thiso is because in displacement time graph slope of graph gives the velocity so for a . Slope is tan30=1/3^1/2, similarly slope of b is tan60=3^1/2. Now ratio of 1/3^1/2 and 3^1/2 is 3/1.
2nd answer isb)24km/have by using formula (2v1×v2)/(v1+v2).
3rd answer isc)37.5km/hr using the above formula.
4th answer is a)60km/hr . Solution: let distance travelled in first half time be d km, then distance travelled in second half will be (60-d)km. Time taken to cover d km = 80×t, time taken to cover second part is (60-d)=40×t. The time is same so d/80=(60-d)/40. Solving this we get d=40 km , so 80-d=20 km. Time taken to cover40km=time taken to cover rest 20km=40/80=20/40=1/2. Avg. Speed =total distance /total time=60km/(1/2+1/2)=60km/hr.

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