# Physics

In the latest Indian Jones film, Indy is supposed to throw a grenade from his car, which is going 43.8 m/s, to his enemy's car, which is going 55.8 m/s. The enemy's car is 15.2 m in front of the Indy's when he lets go of the grenade.

A) If Indy throws the grenade so its initial velocity relative to him is at an angle of 45 above the horizontal, what should the magnitude of the initial velocity be? The cars are both traveling in the same direction on a level road. You can ignore air resistance.

My set up here is
horizontal distance = V * cos45 * Vj * t
[where V is the initial velocity and Vj is Jones' car velocity]

distance between cars = 15.2 + (Vj - Ve) * t
[where Ve is the enemy's car velocity]

I set these two equations equal to each other to find the time it takes the grenade to reach the other car.

(Vcos45)(43.9)(t) = 15.2 + (43.8 - 55.88) * (t)

Then I'm not sure if I'm head in the right direction...

B) Find the magnitude of the velocity relative to the earth.

I'm also not sure how to start this portion.

asked by Kyle
1. Your equations are not correct, but I want to thank you for being one of the very few who show their work here. We wish everyone would do that.

The horizontal distance the grenade travels from the launch point, in earth-based coordinates, is
V*cos45 + Vj*t

The distance between cars is
15.2 + (Ve - Vj)*t = 15.2 + 12.0 t

The way to get t is NOT to set those distances equal.

Consider a coordinate system moving with Jones' car. The grenade moves
V^2/g before hitting the ground when lauched at a 45 degree angle in that coordinate system. The time it takes to hit the ground is
t = 2Vsin45/g.
After that time, the separation of cars is
15.2 + 12 t.
For the grenade to hit the enemy car,
V^2/g = 15.2 + 12*sqrt2*V/g

Solve that quadratic equation for V. Take the posite root.

B) V is relative to the car in which Jones is travelling. Relative to the Earth, add 43.8 m/s to that.

posted by drwls
2. Thank for you the explanation!

But I'd like to ask, how come the last equation isn't

V^2/g = 15.2 + 12(2Vsin45/g)?

posted by Kyle
3. They are the same, since
2 sin 45 = sqrt2

posted by drwls
4. drwls - Your answer isn't correct either. The horizontal distance traveled is V*cos 45*t + Vj*t, and the time it takes for the grenade to reach the ground is SQRT(2Vsin45/g)

posted by Dave
5. Where does V^2/g come from?

posted by Dave

First Name

Your Answer

## Similar Questions

1. ### physics

In the latest Indian Jones film, Indy is supposed to throw a grenade from his car, which is going 79.0 km/h, to his enemy's car, which is going 102 km/h. The enemy's car is 14.3 m in front of the Indy's when he lets go of the
2. ### Physics

In the latest Indian Jones film, Indy is supposed to throw a grenade from his car, which is going 93.0 km/h, to his enemy's car, which is going 130km/h. The enemy's car is 17.0m in front of the Indy's when he lets go of the
3. ### Physics

In the latest Indian Jones film, Indy is supposed to throw a grenade from his car, which is going 93.0 km/h, to his enemy's car, which is going 130km/h. The enemy's car is 17.0m in front of the Indy's when he lets go of the
4. ### College Physics

In the latest Indian Jones film, Indy is supposed to throw a grenade from his car, which is going 93.0 km/h, to his enemy's car, which is going 130km/h. The enemy's car is 17.0m in front of the Indy's when he lets go of the
5. ### Social Studies

My teacher has assigned me to make a new world. I have created a 'enemy' and she said I need a reason the enemy became the enemy. Have any suggestions? I can be disputed territory or ideologies. Another possibility is that the
6. ### Physics

A 4.00 103-kg car has a speed of 9 m/s. The car then hits a tree. The tree doesn't move and the car comes to rest. (a) Find the change in kinetic energy of the car. . J (b) Find the amount of work done in pushing in the front of
7. ### physics

Car A is travelling at 22.0 m/s and car B at 29.0 m/s. Car A is 300 m behind Car B when the drive of car A accelerates his car with an acceleration of2.4 m/s2. How long does it take Car A to overtake Car B?
8. ### Physics

Car A is traveling at 18 m/s and car B at 25 m/s. Car A is 300m behind car B when the driver of Car A accelerates his car with an acceleration of 1.80m/s^2. How long does it take car A to overtake car B?
9. ### Physics

An Indy car with a speed of 120 km/h goes around a level, circular track with a radius of 1 km. What is the centripetal acceleration of the car (in m/s/s)?
10. ### math

six cars are parked in front of a car dealership. If you are looking at the cars from the front. the red car is parked in front of the green car. the black car is between the green and the yellow car. The blue car is parked on the

More Similar Questions